This is one of the webpages of Libarid A. Maljian at the Department of Physics at CSLA at NJIT.

 

 

 

New Jersey Institute of Technology

College of Science and Liberal Arts

Department of Physics

The Earth in Space

Phys 203

Fall 2018

Fifth (Final) Examination lecture notes

 

 

 

All landscapes/environments on planet Earth can be divided into three categories: terrestrial landscapes/environments, marine landscapes/environments, and transitional landscapes/environments.  Terrestrial landscapes/environments are on the continents.  Marine landscapes/environments are at the bottom of the oceans.  Transitional landscapes/environments are shores (where oceans meet continents).  Most of the landscapes/environments on planet Earth are marine, since most of planet Earth is covered with oceans.  Unfortunately, it is precisely for this reason that much is not known about marine landscapes/environments.  We discussed transitional landscapes/environments (shores) earlier in the course.  Therefore, we will spend the rest of the course discussing terrestrial landscapes/environments.

 

Temperatures are hot at and near the Equator, while temperatures are cold at and near the poles.  Humidity is high (aridity is low) at and near the Equator due to the equatorial low.  Humidity is low (aridity is high) at and near roughly thirty degrees latitude (in both hemispheres) due to the subtropical highs.  Humidity is high (aridity is low) at and near roughly sixty degrees latitude (in both hemispheres) due to the subpolar lows.  Finally, humidity is low (aridity is high) at and near the poles due to the polar highs.  Putting all of this together, we conclude that it is hot and humid at and near the equatorial low at the Equator, it is hot and arid at and near the subtropical highs at roughly thirty degrees latitude in both hemispheres, it is cold and humid at and near the subpolar lows at roughly sixty degrees latitude in both hemispheres, and it is cold and arid at and near the polar highs at the poles in both hemispheres.

 

Since it is hot and humid at and near the equatorial low, most terrestrial landscapes/environments at and near the Equator are tropical forests, such as the Amazon rainforest in northern South America, the Congo rainforest in central Africa, and the Indonesian rainforests.  Since it is hot and arid at and near the subtropical highs, most terrestrial landscapes/environments at and near thirty degrees latitude in both hemispheres are hot deserts, such as the Basin and Range in southwestern United States and northwestern Mexico, the Sahara in northern Africa, the Arabian Desert in the Arabian peninsula, the Gobi in China and Mongolia, the Patagonian desert in Argentina, the Kalahari in southern Africa, and the Great Australian Desert in Australia.  Since it is cold and humid at and near the subpolar lows, most terrestrial landscapes/environments at and near sixty degrees latitude in the northern hemisphere are boreal forests (taigas), such as the Canadian boreal forests and the Russian boreal forests.  There are no terrestrial landscapes/environments at and near sixty degrees latitude in the southern hemisphere, but theoretically any such terrestrial landscapes/environments would also be boreal forests (taigas).  Finally, since it is cold and arid at and near the polar highs, most terrestrial landscapes/environments at and near the poles in both hemispheres are permafrost covered with continental ice sheets, such as Antarctica at the South Pole and Greenland near the North Pole.

 

There is a gradual progression of terrestrial landscapes/environments from forests (most humid) to deserts (most arid).  After forests (most humid) would be less humid (or more arid) terrestrial landscapes/environments where there are fewer trees than forests.  These are woodlands.  After woodlands would be less humid (or more arid) terrestrial landscapes/environments where bushes and shrubs could grow but not trees.  These are shrublands.  After shrublands would be less humid (or more arid) terrestrial landscapes/environments where grass could grow but not bushes or shrubs.  These are grasslands.  After grasslands would be less humid (or more arid) terrestrial landscapes/environments just outside of deserts.  These are steppes.  After steppes are deserts, the most arid (least humid) terrestrial landscapes/environments.  Suppose we begin this discussion with deserts, the most arid (least humid) terrestrial landscapes/environments.  After deserts (most arid or least humid) would be less arid (or more humid) terrestrial landscapes/environments.  These are steppes.  After steppes would be less arid (or more humid) terrestrial landscapes/environments where grass could grow.  These are grasslands.  After grasslands would be less arid (or more humid) terrestrial landscapes/environments where bushes or shrubs could grow.  These are shrublands.  After shrublands would be less arid (or more humid) terrestrial landscapes/environments just outside of forests.  These are woodlands.  After woodlands are forests, the most humid (least arid) terrestrial landscapes/environments.

 

Beginning at the tropical forests at the Equator and travelling toward the hot deserts at the subtropical highs, we would encounter tropical forests followed by tropical woodlands followed by tropical shrublands followed by savannas (hot grasslands) followed by hot steppes followed by hot deserts.  If we continue this journey toward the boreal forests (taigas) at the subpolar lows, we would encounter hot deserts followed by midlatitude steppes followed by prairies (midlatitude grasslands) followed by midlatitude shrublands followed by midlatitude woodlands followed by boreal forests (taigas).  This journey would only be theoretical in the southern hemisphere, since there are no terrestrial landscapes/environments at these latitudes in the southern hemisphere.  If we continue this journey toward the permafrost at the polar highs, we would encounter boreal forests followed by subpolar woodlands followed by subpolar shrublands followed by subpolar grasslands followed by tundras followed by permafrost covered with continental ice sheets.  This journey would be mostly theoretical in the southern hemisphere, since there are few terrestrial landscapes/environments at these latitudes in the southern hemisphere.

 

Although the midlatitude seasons (summer and winter) are actually caused by the alternation between more direct sunlight and less direct sunlight due to the obliquity of the Earth as the Earth orbits the Sun, the midlatitude seasons may be interpreted as being caused by the apparent motion of the Sun relative to the Earth.  Although this is not actually the case, it appears to be the case from the frame of reference of the Earth itself.  From this frame of reference, the Sun appears to be on top of the Tropic of Cancer (roughly 23 ˝ degrees north latitude) on roughly June 21 every year.  Over the next six months, the Sun appears to move south, arriving on top of the Equator (zero degrees latitude) three months later on roughly September 21 every year and arriving on top of the Tropic of Capricorn (roughly 23 ˝ degrees south latitude) three months later on roughly December 21 every year.  Over the next six months, the Sun appears to move north, arriving on top of the Equator three months later on roughly March 21 every year and finally returning to the Tropic of Cancer three months later on roughly June 21 every year.  This apparent motion of the Sun may be interpreted as causing the midlatitude seasons (summer and winter).  Note that summer is during June, July, and August in the midlatitudes of the northern hemisphere while summer is during December, January, and February in the midlatitudes of the southern hemisphere.  Conversely, note that winter is during December, January, and February in the midlatitudes of the northern hemisphere while winter is during June, July, and August in the midlatitudes of the southern hemisphere.

 

At and near the Equator, temperatures are hot throughout the year.  Therefore, we do not discuss the seasons as being summer and winter at the tropical latitudes.  The corresponding seasons at the tropical latitudes are the high-sun season and the low-sun season.  The high-sun season is during June, July, and August in the tropical latitudes north of the Equator, while the high-sun season is during December, January, and February in the tropical latitudes south of the Equator.  Conversely, the low-sun season is during December, January, and February in the tropical latitudes north of the Equator, while the low-sun season is during June, July, and August in the tropical latitudes south of the Equator.

 

At and near the poles in both hemispheres, temperatures are cold throughout the year.  Therefore, we do not discuss the seasons as being summer and winter at the polar latitudes.  The corresponding seasons at the polar latitudes are the daytime season and the nighttime season, since entire months can pass with nearly-continuous daytime or nearly-continuous nighttime at these latitudes.  The daytime season is during June, July, and August in the polar latitudes near the North Pole, while the daytime season is during December, January, and February in the polar latitudes near the South Pole.  Conversely, the nighttime season is during December, January, and February in the polar latitudes near the North Pole, while the nighttime season is during June, July, and August in the polar latitudes near the South Pole.

 

As the Sun appears to move relative to the Earth throughout the year, the humidity of forests or the aridity of deserts (as the case may be) moves with the Sun.  In other words, the humidity of forests or the aridity of deserts (as the case may be) intrudes upon neighboring terrestrial landscapes/environments.  For example, consider terrestrial landscapes/environments at the tropical latitudes north of the Equator.  During June, July, and August, the humidity of the tropical forests at the equatorial low intrudes to the north, causing more humid high-sun seasons.  During December, January, and February, the aridity of the hot deserts at the subtropical high (at roughly thirty degrees north latitude) intrudes to the south, causing more arid low-sun seasons.  The situation is somewhat reversed for terrestrial landscapes/environments at the tropical latitudes south of the Equator.  During June, July, and August, the aridity of the hot deserts at the subtropical high (at roughly thirty degrees south latitude) intrudes to the north, causing more arid low-sun seasons.  During December, January, and February, the humidity of the tropical forests at the equatorial low intrudes to the south, causing more humid high-sun seasons.  Although the situation seems to be reversed in the two hemispheres, only the time of year is reversed.  The seasons are actually the same.  High-sun seasons are more humid and low-sun seasons are more arid in the tropical latitudes in both hemispheres.

 

As another example, consider terrestrial landscapes/environments at the midlatitudes in the northern hemisphere.  During June, July, and August, the aridity of the hot deserts at the subtropical high (at roughly thirty degrees north latitude) intrudes to the north, causing more arid summers.  During December, January, and February, the humidity of the boreal forests at the subpolar low (at roughly sixty degrees north latitude) intrudes to the south, causing more humid winters.  The situation is somewhat reversed for terrestrial landscapes/environments at the midlatitudes in the southern hemisphere.  During June, July, and August, the humidity of the boreal forests at the subpolar low (at roughly sixty degrees south latitude) intrudes to the north, causing more humid winters.  During December, January, and February, the aridity of the hot deserts at the subtropical high (at roughly thirty degrees south latitude) intrudes to the south, causing more arid summers.  Although the situation seems to be reversed in the two hemispheres, only the time of year is reversed.  The seasons are actually the same.  Summers are more arid and winters are more humid in the midlatitudes in both hemispheres.  Admittedly, this discussion is only theoretical for the southern hemisphere, since there are no terrestrial landscapes/environments at these latitudes in the southern hemisphere.

 

As yet another example, consider terrestrial landscapes/environments at the polar latitudes near the North Pole.  During June, July, and August, the humidity of the boreal forests at the subpolar low (at roughly sixty degrees north latitude) intrudes to the north, causing more humid daytime seasons.  During December, January, and February, the aridity of the permafrost at the polar high (at the North Pole) intrudes to the south, causing more arid nighttime seasons.  The situation is somewhat reversed for terrestrial landscapes/environments at the polar latitudes near the South Pole.  During June, July, and August, the aridity of the permafrost at the polar high (at the South Pole) intrudes to the north, causing more arid nighttime seasons.  During December, January, and February, the humidity of the boreal forests at the subpolar low (at roughly sixty degrees south latitude) intrudes to the south, causing more humid daytime seasons.  Although the situation seems to be reversed in the two hemispheres, only the time of year is reversed.  The seasons are actually the same.  Daytime seasons are more humid and nighttime seasons are more arid in the polar latitudes in both hemispheres.  Admittedly, this discussion is mostly theoretical for the southern hemisphere, since there are few terrestrial landscapes/environments at these latitudes in the southern hemisphere.

 

There are many other effects that we have neglected in the preceding discussion, such as ocean-current effects, marine-versus-continental effects, and orographic effects.  As a result, there are many exceptions to the preceding discussion.  This having been said, the preceding discussion is mostly correct.  This reveals that latitude is the primary variable determining the characteristics of terrestrial landscapes/environments, while ocean-current effects, marine-versus-continental effects, and orographic effects are secondary (but still important) variables determining the characteristics of terrestrial landscapes/environments.

 

High mountaintops are terrestrial landscapes/environments that belong in their own category.  Consider a tall mountain at the Equator.  At the base of the mountain, we have a tropical forest, since we are at the equatorial low.  However, the temperature gradually becomes colder as we climb the mountain.  Eventually, the temperature may be so cold that we have a boreal forest.  If the mountain is tall enough, we would encounter subpolar woodlands at higher elevations and subpolar shrublands at even higher elevations.  If the mountain is tall enough, we reach an elevation where bushes and shrubs can no longer grow.  This is the timberline, more commonly known as the tree line.  At higher elevations we encounter subpolar grasslands, and at even higher elevations we encounter tundras.  If the mountain is tall enough, the summit of the mountain will be permafrost covered with a glacier, even though the mountain is at the Equator where the sea-level temperature is quite hot!  This discussion reveals that elevation up a mountain is analogous to latitude.  We can turn this logic completely around and assert that latitude is analogous to elevation up a mountain.  We may even go so far as to claim that the entire planet Earth has a timberline, an extreme latitude in each hemisphere beyond which bushes and shrubs can no longer grow, just as there is an extreme elevation up a mountain beyond which bushes and shrubs can no longer grow.  A splendid example of this correspondence between latitude and elevation up a mountain is the term icecap.  Summits of tall mountains are called icecaps if they are permafrost covered with glaciers, and poles of planets are also called icecaps if they are permafrost covered with ice sheets.

 

Geomorphology is the study of how and why landscapes/environments change, and a geomorphologist is someone who studies the evolution of landscapes/environments.  A geomorphic agent is anything that changes landscapes/environments.  For example, wind can change landscapes/environments.  The technical term for the action of wind as a geomorphic agent is aeolian processes, named after Aeolus the Greek god of wind.  Gravity can change landscapes/environments by pulling rocks and sediments downward.  The technical term for the action of gravity as a geomorphic agent is mass wasting.  Running water (rivers and streams) can change landscapes/environments.  The technical term for the action of running water as a geomorphic agent is fluvial processes.  Underground water can change landscapes/environments.  The technical term for the action of underground water as a geomorphic agent is groundwater processes.  Glaciers (giant masses of ice) can change landscapes/environments.  The technical term for the action of glaciers as a geomorphic agent is glacial processes.  Although there are many more geomorphic agents, these five (fluvial processes, groundwater processes, glacial processes, aeolian processes, and mass wasting) are the most important geomorphic agents.  By far, the single most important geomorphic agent is fluvial processes.  Nothing changes landscapes/environments more dramatically in a shorter amount of time than rivers and streams.

 

When any geomorphic agent changes a landscape/environment, it first destroys the existing landscape/environment.  This is called degradation.  More technically, degradation is the action of breaking down rocks into sediments.  Next, the geomorphic agent transports (moves) these sediments from one location to another.  This is called erosion.  Finally, the geomorphic agent uses these sediments to build a new landscape/environment.  This is called aggradation.  To summarize, any geomorphic agent first degrades a landscape/environment into sediments, then erodes these sediments to another location, then finally aggrades a new landscape/environment from these sediments.

 

Another term for degradation is weathering.  The two main types of weathering are mechanical weathering and chemical weathering.  Chemical weathering is the degradation of landscapes/environments with compositional changes in the rocks and sediments, while mechanical weathering is the degradation of landscapes/environments without compositional changes in the rocks and sediments.  Mechanical weathering is always executed through the action of physical forces.  There are many examples of mechanical weathering, including frost wedging, salt wedging, and exfoliation.  There are many examples of chemical weathering, including carbonation, oxidation, and hydrolysis.

 

Chemical weathering requires some understanding of acids and bases.  According to the Arrhenius theory of acids and bases, an acid is a solution with an excess of hydronium cations (H3O+), while a base is a solution with an excess of hydroxide anions (OH).  Also according to this Arrhenius theory, the reaction of an acid and a base yields a salt plus water.  According to the Brřnsted-Lowry theory of acids and bases, an acid is still a solution with an excess of hydronium cations, but a base is a solution that is deficient of hydronium cations.  Also according to this Brřnsted-Lowry theory, the reaction of an acid and a base yields the acid’s conjugate base plus the base’s conjugate acid.  According to the Lewis theory of acids and bases, an acid is a solution that is deficient of electron pairs, while a base is a solution with an excess of electron pairs.  Regardless of which theory we use, the pH is a measure of whether a solution is an acid or a base.  An acid has a pH that is less than seven, while a base has a pH that is greater than seven.  Only pure water has a pH exactly equal to seven.  For example, carbonation is the dissolving of carbon dioxide into water yielding carbonic acid, a solution with a pH less than seven.  Whenever it rains, the naturally-occurring carbon dioxide in the atmosphere has dissolved within the raindrops, making the rain acidic.  Note that this is naturally-occurring.  In other words, even in the complete absence of human pollution, naturally-occurring unpolluted rain water is actually carbonic acid.

 

There are still other types of weathering.  Biological weathering is the degradation of landscapes/environments by lifeforms.  Differential weathering is the degradation of different parts of a landscape/environment at varying rates.  Common landforms resulting from differential weathering are inselbergs (such as Zuma Rock in Niger State, Nigeria) and volcanic necks (such as Shiprock in New Mexico, United States).

 

As a result of weathering of all kinds, nearly the entire surface of planet Earth is covered with a thin layer of sediments commonly called dirt or ground or earth.  The technical term for this thin layer of sediments is regolith, derived from the Greek words for blanket and rock.  As far as the survival of the human species is concerned, the most important type of regolith is soil.  Thousands of years ago when the population of the species was small, humanity was able to survive nomadically (randomly gathering plants and randomly killing animals for food).  However, roughly six thousand years ago the population of the human species became large enough that agriculture became necessary for its survival.  Agriculture is the domestication of plants and animals near a supply of “fresh” water to provide a steady source of food, and agriculture is impossible without soil.  For this reason, a discussion of soil sciences is now in order.

 

Soil is a particular type of regolith that is a mixture of inorganic minerals, air, water, and organic materials (both living and decomposing).  Recall that the geosphere is the solid inorganic part of the Earth, the atmosphere is the sum total of all air of the Earth, the hydrosphere is the sum total of all water of the Earth, and the biosphere is the sum total of all life of the Earth.  Since soil is a mixture of inorganic minerals, air, water, and organic materials (both living and decomposing), this means that soil is the intersection of the geosphere, the atmosphere, the hydrosphere, and the biosphere.  The sum total of all soil of the Earth is the pedosphere.  In other words, the pedosphere is where all the other Earth spheres meet one another.

 

Recall that according to the Wentworth Scale, the largest sediments are gravels, smaller sediments are sand, smaller sediments are silt, and the smallest sediments are clay/mud.  The texture of soil is determined by its inorganic mineral component.  Soil will feel more coarse-grained if its mineral components are large (sand).  Soil will feel more fine-grained if its mineral components are small (clay/mud).  Soil will feel intermediate between these extremes if its mineral components are between large and small (silt).  Soil with roughly equal mixtures of sand, silt, and clay/mud is called loam.

 

The classification of the water part of soil is as follows.  Water falling into the soil from rain for example is called free water.  This free water may then begin to attract itself.  This is called the water of cohesion.  Water that sticks to inorganic or organic parts of the soil is called the water of adhesion.  Finally, water that has completely merged with the inorganic or organic part of the soil is called the combined water.

 

The degradation of one part of the soil is called eluviation.  The erosion of this material from one part of the soil to another part of the soil is called leaching.  The aggradation of a new part of the soil from this material is called illuviation.  To summarize, just as geomorphological processes in general begin with degradation then follow with erosion then end with aggradation, geomorphological processes in soil begin with eluviation then follow with leaching then end with illuviation.

 

Eluviation, leaching, and illuviation develop layers of soil, which are called soil horizons.  The uppermost layer of soil is the A horizon, commonly known as the topsoil.  Below the A horizon is the B horizon, commonly known as the subsoil.  Below the B horizon is the C horizon, and below the C horizon is what is commonly known as the bedrock.  Although this bedrock is not part of the soil, many soil scientists call it the R horizon, meaning the rock horizon.  On top of the A horizon is a layer of dead plants and animals that have not yet decomposed.  This is commonly known as the litter.  Although this litter is not yet part of the soil, many soil scientists call it the O horizon, meaning the organic horizon.  This O horizon decomposes and ultimately creates the A horizon.  To summarize, first we have the O horizon below which is the A horizon below which is the B horizon below which is the C horizon below which is the R horizon.  Eluviation usually but not always occurs in the A horizon, leaching usually but not always occurs from the A horizon to the B horizon, and illuviation usually but not always occurs in the B horizon.

 

Although the quality of the parent material does affect whether or not soil will be agriculturally productive, the most important factor affecting soil quality is climate.  Soil derived from poor parent material will nevertheless yield a productive crop if it is in a good climate, while soil derived from good parent material will nevertheless yield a poor crop if it is in a bad climate.  (We will make clear which climates are good for agriculture and which climates are bad for agriculture in a moment.)  Another factor affecting soil quality is the topography of the land.  Yet another factor affecting soil quality is the abundance of living plants and animals within the soil.  Such lifeforms mix the soil, thus rejuvenating formerly dead soil.  This process is called bioturbation.  Although prairie dogs are efficient at bioturbation, earthworms are much more important.  As earthworms dig through soil, they eat the soil, extract water and minerals for their survival from the soil, and excrete water and minerals harmful to their survival back into the soil.  As a result, earthworms can completely rejuvenate dead soil in a relatively short amount of time.  It is not an exaggeration to say that the health of soil can be determined by digging up some of the soil and simply counting the number of living earthworms within it.  Rapid bioturbation of soil is essential to rejuvenating dead soil quickly so that farmers are able to continually produce large amounts of crop to feed the billions of members of the human species.  Therefore, it is not an exaggeration to conclude that the single most important animal necessary for the survival of the human species is the earthworm.

 

Taxonomy is the study of classification.  In biological taxonomy, all lifeforms are categorized into five biological kingdoms.  Each biological kingdom is subdivided into several biological phyla.  Each biological phylum is subdivided into several biological classes.  Each biological class is subdivided into several biological orders.  Each biological order is subdivided into several biological families.  Each biological family is subdivided into several biological genera.  Finally, each biological genus is subdivided into several biological species.  Whereas there are only five biological kingdoms, by the time we get to biological species there have been so many subdivisions that there are millions of biological species that have been classified.  Soil taxonomy is very much similar.  All soils are categorized into twelve soil orders.  Each soil order is subdivided into several soil suborders.  Each soil suborder is subdivided into several soil great groups.  Each soil great group is subdivided into several soil subgroups.  Each soil subgroup is subdivided into several soil families.  Finally, each soil family is subdivided into several soil series.  Whereas there are only twelve soil orders, by the time we get to soil series there have been so many subdivisions that there are more than nineteen thousand soil series that have been classified.  Whereas it is impossible to discuss all of the soil series, discussing all twelve of the soil orders provides tremendous insight into soil morphology.

 

Consider soils that have just been born so that no eluviation, leaching, or illuviation has taken place.  These are the entisols, the youngest soil order.  The word entisol is derived from the words recent and soil.  In other words, entisols are recently-born soils.  Now suppose some eluviation, leaching, and illuviation has taken place so that the soil has horizons, although they are still immature horizons.  These are young soils, and six soil orders are in this category: andisols, aridsols, gelisols, histosols, inceptisols, and vertisols.  The andisols are the volcanic ashes.  The word andisol is derived from the Andes Mountains where there is active vulcanism.  The aridsols are soils found in deserts.  The word aridsol is derived from the word arid, which means dry.  The gelisols are the soils above permafrost.  Eluviation, leaching, and illuviation are not primarily due to bioturbation in gelisols but due to cryoturbation, also known as frost churning.  The histosols are organically-rich soils found in wetlands (swamps, marshes, and quagmires).  Now suppose these young soils are subjected to even more eluviation, leaching, and illuviation.  The soil thus develops mature horizons, and these soils are the best soils for agriculture.  There are two soil orders in this category: the alfisols and the mollisols.  These two soil orders are found abundantly in the midwestern United States, which is precisely why the midwestern United States produces enough food to feed the entire world.  These soils are so rich that they have a deep black color.  You are strongly urged to take a road trip across the United States so that you can see these soils with your own eyes.  You will also see with your own eyes that the most abundant crop produced in the United States (and the entire world) is corn, with no other crop being produced anywhere nearly as abundantly.  Now suppose these soils are subjected to even more eluviation, leaching, and illuviation.  The result is old, dying soils.  There are two soil orders in this category: the spodosols and the ultisols.  The word ultisol is derived from the words ultimate and soil.  Unfortunately, this is not exactly correct since this soil is not quite a dead soil.  When soil is subjected to a maximum amount of eluviation, leaching, and illuviation, the soil is dead.  These are the oxisols, the oldest soil order.  These oxisols are found in tropical forests at the equatorial low where there is the most amount of rain in the entire world.  Since woodlands are just outside of forests, the spodosols and the ultisols are found in woodlands where the precipitation is high but not as high as in forests.  To summarize, the youngest soil order is the entisols, the slightly older but still immature soil orders are the andisols, aridsols, gelisols, histosols, inceptisols, and vertisols, the mature soil orders that are best for agriculture are the alfisols and mollisols, the dying yet still alive soil orders are the spodosols and ultisols, and the oldest soil order is the oxisols.  The best soils for agriculture are the alfisols and the mollisols, while the worst soils for agriculture are the entisols (since these are the newly born soils) and the oxisols (since these are the dead soils).

 

Mass wasting is the action of gravity as a geomorphic agent.  Mass-wasting events are commonly called landslides, but this is not a word used in technical geomorphology.  There are many different ways a mass-wasting event can be triggered, such as heavy rains, snowmelts, seismic activity (such as earthquakes), and forest fires.  However, no such violent event is even necessary to trigger a mass-wasting event.  A mass-wasting event may be caused by an over-steepened slope.  The maximum steepness that a hillside or mountainside can endure before gravity can finally move regolith downward is called the angle of repose.  In other words, the moment the aggrading of sediments upon a hillside or mountainside results in a steepness greater than the angle of repose, gravity will degrade the hillside or mountainside.  The regolith will move downward.

 

The fastest type of mass-wasting event is called a fall.  Somewhat slower than a fall is a slide or flow.  Finally, the slowest type of mass-wasting event is called creep (or solifluction when glacier-related).  The regolith moving during a mass-wasting event may be primarily rock, debris, earth, or mud.  An avalanche is a mass-wasting event that is not necessarily glacier-related, since there are rock avalanches and mud avalanches.  An avalanche that is glacier-related should properly be called a snow avalanche.  A lahar is a mudflow composed of pyroclastic materials down the side of a volcano.

 

After many mass-wasting events, there may be an accumulation of sediments at the base of a hill or mountain.  These are called talus slopes, and the sediment itself is called talus.  A mass-wasting event may leave behind a steep cliff.  These steep cliffs are often called scarps, but they are more properly called escarpments.

 

The action of rivers and streams as a geomorphic agent is called fluvial processes.  This is the single most important geomorphic agent in general.  Nothing changes a landscape/environment more dramatically in a shorter period of time than rivers and streams.  This is remarkable considering that water in rivers and streams makes up a tiny fraction of all the water in the hydrosphere.  Roughly ninety-seven percent of all the water in the hydrosphere is in the oceans, and the remaining three percent is in giant glaciers called continental ice sheets.  Much, much less than one percent of all the water in the hydrosphere is in the air as water vapor, underground as groundwater, and on the continents in lakes, rivers, and streams.  Nevertheless, the running water in rivers and streams is the single most important geomorphic agent, in general.  The water cycle, more properly called the hydrologic cycle, is the continuous motion of water from one part of the Earth to another.  Evaporation is the transfer of water from the hydrosphere to the atmosphere, precipitation is the transfer of water from the atmosphere onto the geosphere, and runoff together with infiltration is the transfer of water from the geosphere back to the hydrosphere.  In addition, water is transferred from the biosphere to the atmosphere through transpiration.

 

We begin our discussion of fluvial processes with a basic discussion of running water.  Precipitation on or near a mountaintop or glacial meltwater near a mountaintop begins the river.  This is the head of the river.  Water flows down the mountain along rills that merge to form brooks or creeks.  These brooks or creeks eventually merge to form streams which eventually merge to form rivers.  Rivers may merge to form even larger rivers.  Eventually, the river ends at the ocean or some other large body of water.  This is called the mouth of the river.  To summarize, the head of the river is rills that merge to form brooks or creeks that merge to form streams that merge to form rivers that merge to form large rivers ending at the mouth of the river.  The generic word for a rill, a brook or a creek, a stream, or a river is a watercourse.  A smaller watercourse that feeds water into a larger watercourse is called a tributary.  In other words, rills are tributaries of brooks or creeks, brooks or creeks are tributaries of streams, streams are tributaries of rivers, and rivers can be tributaries of larger rivers.  The opposite of a tributary is a distributary, which is a smaller watercourse that takes water out of a larger watercourse.

 

The pattern with which smaller watercourses merge to become larger watercourses is called a drainage pattern.  The most common type of drainage pattern is the dendritic drainage pattern.  The word dendritic means treelike.  If you were to look at a dendritic drainage pattern from an airplane flying overhead, the river would look like the trunk of a tree, the streams would look like large branches attached to the trunk, and the brooks or creeks would look like small branches attached to the large branches.  There are other drainage patterns as well.  The radial drainage pattern is found around steep mountains and volcanoes, the rectangular drainage pattern is found in weathering-resistant rocks that have been faulted, and the trellis drainage pattern is found in landscapes/environments with both weathering-susceptible rock and weathering-resistant rock.  All of these drainage patterns apply to perennial rivers, more commonly known as permanent rivers.  The opposite of a perennial river is an ephemeral river, more commonly known as a temporary river.  The drainage pattern associated with ephemeral rivers is the interior drainage pattern.

 

The total area of land that feeds water into a watercourse is the watershed of the watercourse.  A watershed is also known as a drainage basin.  The watershed or drainage basin of a rill may be smaller than a room.  However, the watershed of a brook or creek will be larger, the watershed of a stream will be even larger, and the watershed of a river will be larger still.  The watersheds of the largest rivers in the world take up enormous areas of continents.  For example, it is not an exaggeration to say that the Mississippi River watershed is the entire area of the United States between the Appalachian Mountains and the Rocky Mountains.  The boundary between two watersheds is called a drainage divide.  A drainage divide between two enormous watersheds is called a continental divide, since one of the enormous watersheds feeds one ocean while the other enormous watershed often feeds a different ocean.

 

The river gradient is commonly considered to be the steepness of a river.  More correctly, the river gradient is the vertical drop of a river divided by the horizontal distance of the river.  For example, if a river drops by one hundred feet over a horizontal distance of twenty miles, then the river gradient is five feet per mile (since one hundred divided by twenty is five).  The river gradient is typically steepest at the head but becomes more and more shallow downstream, ultimately becoming most shallow at the mouth.  In other words, the river gradient typically decreases from the head to the mouth.  The longitudinal profile is a graph of the river gradient from the head to the mouth.

 

The river discharge is commonly considered to be the amount of water flowing in the river combined with how fast the water is flowing.  More correctly, the river discharge is the volume of water flowing per unit time.  The river discharge is typically smallest at the head and becomes greater and greater downstream, ultimately becoming greatest at the mouth.  In other words, the river discharge typically increases from the head to the mouth.  This is for two reasons.  Firstly, there is more and more water downstream as smaller watercourses merge to form larger watercourses.  Secondly, water moves faster downstream since gravity has pulled it downhill.

 

Through the action of both mechanical weathering and chemical weathering, running water carves out a river channel for itself.  The sides of the river channel are called the river banks, and the bottom of the river channel is called the river bed.

 

The rocks and sediments that a river erodes is called the river load.  The largest river load is called the bed load, since this load is so heavy that it rolls, slides, or bounces at the bottom of the river channel (the river bed).  Smaller than the bed load is the suspended load.  These are sediments that are light enough to be carried by the running water.  The smallest river load is the solution load.  This is river load so small that it is completely dissolved within the water.

 

The competence of a river is the maximum size load that the river erodes, while the capacity of a river is the total amount of load that the river erodes.  These two concepts sound like the same thing, but they are completely different.  For example, it is entirely possible for a river to have a large competence but small capacity.  It is also possible for a river to have a small competence but large capacity.  As a concrete example, consider two rivers.  The first river has such a large competence that it is able to erode bed load.  The river may even look brown and dirty from the large load being eroded.  Now suppose the second river has such a low competence that it is only able to erode solution load, which cannot be seen since it is completely dissolved.  The river may actually look clean and clear.  Although the first river definitely has a larger competence and the second river definitely has a smaller competence, no conclusion can be drawn about the capacities.  It is entirely possible that the total amount of solution load of the second river may add up to a larger amount than the bed load in the first river.  In other words, a river that looks clean and clear may in fact be eroding a large amount of load.  To go further, we can never draw the conclusion that a river is not eroding any load.  Every river, without exception, is eroding some capacity of load.

 

We now begin a thorough discussion of fluvial geomorphology.  Throughout this discussion, we will appreciate how dramatically running water changes landscapes/environments.  First, the running water will try to carve out a longitudinal profile so that it will take the least amount of time to travel from the head to the mouth.  Most people believe that the path of least time between two points is a straight line, but in the presence of gravity this is not correct.  The geometrical question of finding the path of least time between two points in the presence of a constant force such as gravity is such a difficult geometrical question that it was solved somewhat recently, only about three hundred years ago.  This mathematical problem is called the brachistochrone problem, and the solution to the brachistochrone problem is a cycloid, or more correctly an arc of an inverted cycloid.  In other words, the path of least time between two points in the presence of a constant force such as gravity is an arc of an inverted cycloid.  Therefore, running water will carve out a longitudinal profile that looks like the arc of an inverted cycloid.  This explains why the river gradient is steepest at the head and becomes less steep (more shallow) downstream, becoming most shallow at the mouth.  An arc of an inverted cycloid starts out steep and ends up shallow.  The bottom of such a longitudinal profile is called the base level of the river.

 

If all of the rock from the head to the mouth had uniform (constant) resistance to weathering, this would summarize the entire development of the longitudinal profile of a river.  However, this is obviously not the case.  The running water carves out the arc of an inverted cycloid until it encounters more weathering-susceptible rock, at which point the water will dig downward to carve out another inverted cycloid.  This process is called downcutting.  The running water may eventually encounter even more weathering-susceptible rock, at which point downcutting happens again.  We now see that the longitudinal profile is actually a collection of inverted cycloids, and two neighboring cycloids will join where the river gradient changes abruptly from shallow to steep.  Here, running water will approach with laminar flow (orderly flow) but will then fall down and crash with turbulent flow (disorderly flow).  This part of the river is called a waterfall, since the water falls downward.  In other words, a waterfall is located at a base level of a particular inverted cycloid where the river gradient abruptly changes.  This is called a local base level, since the base level of the very last inverted cycloid at the mouth of the river is called the ultimate base level.  Through mechanical weathering and chemical weathering, a waterfall will gradually smooth out the abrupt change in the river gradient at its local base level, causing the water to eventually fall down less abruptly.  In other words, waterfalls eventually become more mild waterfalls, and these mild waterfalls are called rapids.  To summarize, waterfalls are located at local base levels with abrupt changes in the river gradient, and waterfalls eventually become rapids, which are located at local base levels with less abrupt changes in the river gradient.

 

Once the longitudinal profile is fairly developed, the energy of the running water begins to develop the lateral profile.  In other words, the running water begins to change the landscapes/environments on both sides of the river.  Consider waterfalls or rapids that flow over a narrow river valley.  Mass wasting will cause rocks to fall down, and the narrow river valley eventually becomes a wide river valley.  Now suppose at the bottom of this river valley the river channel is straight.  The water in this straight channel will not flow straight however, since it must maneuver around sand deposits within the river channel.  The flow therefore follows a curved path, even though the river channel is straight.  The deepest part of a river channel is the thalweg, which is almost never straight even if the river channel is straight.  (By international agreement, the border between two countries separated by a river is not just the river itself.  The precise border is the thalweg of the river.  This international agreement is called the thalweg doctrine or the thalweg principle.)  Since the water follows a curved path to maneuver around the sand deposits, the actual shape of the river channel changes as the water cuts into the outer banks of the river channel leaving the sand deposits on the inner banks of the river channel.  The straight river channel has become a sinuous river channel.  The curves in the river channel become even more severe as the water cuts into the outer bank of every curve.  The sinuous river channel has become a meandering river channel.  The word meander means to walk aimlessly (without a logical direction).  In other words, the curves in meandering river channels are so severe that it seems as if the water curved randomly without any logical reason.  To summarize, straight river channels become sinuous river channels which eventually become meandering river channels.  These meandering river channels cut into the surrounding wide river valley, making it wider and wider until the river has carved out a vast flat area of land around itself.  This is called a floodplain, since this entire area will be flooded if the river overflows by even a small amount.  To summarize the development of the lateral profile around a river, we begin with narrow river valleys which then become wide river valleys which eventually become floodplains.

 

A river may overflow rather periodically, causing the floodplain around it to flood regularly.  Remarkably, the river aggrades landforms that protect its own floodplain.  For example, each time there is flooding, it is not just water that overflows from the river but the load that it erodes also overflows.  Some of this load may be deposited on the river banks.  With each flooding, more and more of these rocks and sediments accumulate on the river banks until walls of rock have been built that prevent the water from further flooding the floodplain.  These are sometimes called levees, but they are more properly called natural levees to distinguish them from artificial levees that are built by humans.  There is, however, a disadvantage of natural levees.  If there happens to be so much flooding one year that the water actually floods over the levees, then the levees will prevent water from draining back into the river.  The result is a backswamp on either side of the river.  The water in a backswamp may try to take its own path to the ocean (or major body of water).  The result is a yazoo tributary, a smaller river that runs parallel to a major river since it is being prevented from being a tributary to the major river.  The word yazoo is derived from the Yazoo River, which is itself a yazoo tributary of the Mississippi River.  Another means by which rivers protect their own floodplains is through connections between meanders.  These are sometimes called cutoffs, but they are more properly called natural cutoffs to distinguish them from artificial cutoffs that are carved out by humans.  A natural cutoff enables the water to take a shorter path to the ocean (or major body of water) thus decreasing the time that the floodplain is flooded.  Once a natural cutoff forms, a meander will become an oxbow lake, the oxbow lake will then become an oxbow swamp, and the oxbow swamp will eventually become a meander scar.

 

Floods are the most common and most destructive of all natural disasters.  Humans attempt to control flooding through artificial levees and artificial cutoffs.  The digging of artificial cutoffs is called channelization.  For example, the United States Army Corps of Engineers has used channelization to shorten the length of the Mississippi River by more than two hundred and forty kilometers (one hundred and fifty miles) in order to ease flooding in the midwestern United States.  Most deaths due to flooding in the United States are automobile-related.  For your own safety, never ever drive through a road that is flooded.  Wait for the flood to completely subside first.  Again, most deaths in the United States due to flooding, which is itself the most common and most destructive of all natural disasters, is automobile-related.

 

Groundwater processes is another important geomorphic agent.  While there are actual underground rivers as depicted in movies and while such underground rivers are indeed valid examples of groundwater, the vast majority of all groundwater is not of this type.  The vast majority of all groundwater flows through the solid rock beneath us.  Any rock whatsoever is not entirely solid.  A certain amount of the space of any rock is empty.  The fraction of the volume of a rock that consists of empty space is called the porosity of the rock.  The degree to which a rock is able to transmit water through it is called the permeability of the rock.  These two concepts sound like the same thing, but they are different.  For example, it is entirely possible for a rock to have a large porosity but small permeability.  It is also possible for a rock to have a small porosity but large permeability.  All rocks have a certain amount of porosity, and all rocks have a certain amount of permeability.  Therefore, water is able to flow through rock, and the vast majority of all groundwater is of this type.

 

If you were to drill into the ground, you would eventually reach a layer of rock that is completely filled with water flowing through it.  This is the phreatic zone, commonly known as the zone of saturation.  The word saturated means filled.  In other words, the zone of saturation is rock that is filled with flowing water.  Above this layer is the vadose zone, commonly known as the zone of aeration.  The word aerated means exposed to air.  In other words, the zone of aeration is rock that is not filled with water (that still has some air within its pores).  Between these two zones is the water table.  To summarize, if we were to drill into the ground, first we would encounter the vadose zone (the zone of aeration), then we would encounter the water table, then we would encounter the phreatic zone (the zone of saturation).

 

Layers of rock that are highly porous and permeable to groundwater are called aquifers, commonly composed of conglomerate, sandstone, faulted igneous rock, or faulted metamorphic rock.  Layers of rock that are highly nonporous and impermeable to groundwater are called aquitards, commonly composed of siltstone, shale, unfaulted igneous rock, or unfaulted metamorphic rock.  An aquifer between two aquitards is called a confined aquifer.  The buildup of pressure within a confined aquifer may eventually shoot groundwater out of the ground.  These are called artesian wells.

 

Although fluvial processes is the single most important geomorphic agent in general, there are certain landscapes/environments where groundwater processes are more important as compared with other geomorphic agents.  One such landscape/environment is the karst topography, where we find caverns (caves), natural bridges, sinkholes (natural wells), springs, artesian wells, hot springs, and geysers.  Speleology is the study of caverns (caves), and a speleologist is someone who studies caverns (caves).  A speleothem is any rock formation whatsoever found within caverns.  Long and skinny speleothems that grow from cavern ceilings are called stalactites, while short and fat speleothems that grow from cavern grounds are called stalagmites.  A stalactite and a stalagmite may eventually merge becoming one speleothem connecting the cavern ceiling to the cavern ground.  These speleothems are called columns.

 

Aeolian processes is another important geomorphic agent.  This is the action of wind as a geomorphic agent.  Aeolian processes are more important in deserts as compared with other geomorphic agents, although it should again be emphasized that fluvial processes is the single most important geomorphic agent, even in deserts.  For example, an ephemeral river that forms after rain may last only a few minutes, but it nevertheless sculpts the desert more than the action of the wind over the rest of the entire year.  Nevertheless, whereas aeolian processes may not be the most important geomorphic agent in deserts, aeolian processes are more important in deserts as compared with other landscapes/environments.

 

It is a common misconception that deserts are entirely sand.  Not only is this false, deserts are not even mostly sand.  For example, the Sahara in northern Africa is the largest hot desert in the world.  Nevertheless, only about ten percent of the Sahara is covered with sand; ninety percent of the Sahara is not covered with sand.  As another example, the sandiest desert in the world is the Arabian Desert.  Nevertheless, this sandiest desert in the world is only one-third covered with sand; two-thirds of the Arabian Desert is not covered with sand.  The parts of a desert covered with solid rocks are called hamadas, the parts of a desert covered with gravels are called regs, and the parts of a desert covered with sands are called ergs.

 

Just as the sediments eroded by running water is called fluvial load, the sediments eroded by wind is called aeolian load.  Gravels are too heavy to be eroded by wind; consequently, gravels are not part of aeolian load.  Although sands are smaller and lighter than gravels, they are still heavy enough that as wind blows the sands roll, slide, or bounce upon the ergs of the desert.  For this reason, sands are considered aeolian bed load, in perfect analogy with fluvial bed load.  Finally, silts are small enough and light enough that they can actually be carried by the wind.  For this reason, silts are considered aeolian suspended load, in perfect analogy with fluvial suspended load.

 

A small rock that has been smoothed by the action of the wind is called a ventifact, and a large rock that has been smoothed by the action of the wind is called a yardang.  Entire landscapes/environments are degraded by aeolian processes.  A plateau is a large area of land with high elevation but shallow relief.  As winds degrade the plateau, it becomes smaller and smaller over time.  The plateau is worn down to a mesa.  As winds continue to degrade the mesa, it becomes smaller and smaller over time.  The mesa is worn down to a butte.  To summarize, aeolian processes degrade plateaus into mesas and degrade mesas into buttes.

 

The final geomorphic agent to discuss in this course is glacial processes.  The sum total of all ice of the Earth is called the cryosphere.  Giant masses of ice that sculpt entire mountains and valleys are called alpine glaciers, but even these are small compared to continental ice sheets, enormous masses of ice that are the sizes of entire continents or microcontinents.  Continental ice sheets only exist on planet Earth during ice ages.  As we discussed earlier in this course, planet Earth entered into an ice age roughly thirty million years ago that continues to this day.  During glacial periods of the current ice age, continental ice sheets expand beyond the poles, while during interglacial periods of the current ice age, continental ice sheets retreat back to the poles.  We are currently within an interglacial period of the current ice age.  Consequently, there are presently only two continental ice sheets on this planet.  One covers the continent Antarctica at the South Pole.  This continental ice sheet is the single largest mass of ice in the entire world; ninety percent of all the ice in the cryosphere makes up that continental ice sheet.  The remaining ten percent of all the ice in the cryosphere is in the other continental ice sheet that covers the microcontinent Greenland near the North Pole.  All of the alpine glaciers in the world combined add up to a small fraction of the ice in the cryosphere.  Continental ice sheets are so enormous that entire mountain ranges are buried beneath them.  These buried mountain ranges are called nunataks.  Continental ice sheets expand over the ocean waters that surround the continent or microcontinent.  These intrusions are called ice shelves.  The Ross Ice Shelf is the largest ice shelf in the world.  Pieces of an ice shelf may break off resulting in giant slabs of ice floating in the ocean.  These are called ice floes.  Whereas the study of continental ice sheets, ice shelves, and ice floes is interesting, there are only two continental ice sheets on this planet presently, and there would be none if planet Earth were not presently within an ice age.  There are thousands of alpine glaciers all over planet Earth on every continent (except Australia), and these alpine glaciers would exist whether or not planet Earth were within an ice age.  Therefore, we will henceforth concentrate our attention on alpine glaciers.

 

We begin with the formation of a glacier.  Consider precipitation upon a high mountaintop.  The mountaintop is so high that the precipitation is solid.  This precipitation is called normal ice.  As normal ice accumulates, the weight of the abundance of this normal ice begins to squeeze out the air within itself.  The ice eventually becomes firn, a high-density form of ice with the consistency of course sand.  As even more ice accumulates, the firn is still further compressed until it becomes glacial ice, an extremely high-density form of ice that flows somewhat like a liquid.  Although most of a glacier is made of glacial ice, the uppermost layer of a glacier is made of normal ice since it has no overlying weight to compress it to exotic densities.  This uppermost layer of a glacier is sometimes called the glacial crust, but it is more properly called the zone of fracture, since normal ice can break.  Cracks within this zone of fracture are called glacial crevasses.  Since the zone of fracture is roughly fifty meters thick (roughly one hundred and sixty feet thick), many glaciologists surveying glaciers have been killed while walking upon the zone of fracture and then falling into a glacial crevasse.

 

The beginning of a glacier is called the glacial head, in perfect analogy with the beginning of a river being called the river head.  However, while the end of a river is called the river mouth, the end of a glacier is called the glacial terminus.  At and near the glacial terminus, the glacier loses mass through melting, subliming, and calving.  Calving is the processes by which pieces of a glacier break and fall into the ocean becoming mountains of floating ice called icebergs.  Any process by which a glacier loses mass is called glacial ablation.  In other words, melting, subliming, and calving are the three different forms of glacial ablation.  The zone of accumulation of a glacier is the region at and near its head where the glacier gains more mass than it loses.  The zone of wastage of a glacier is the region at and near its terminus where the glacier loses more mass than it gains.  The boundary between the zone of accumulation and the zone of wastage is called the equilibrium line.

 

When a glacial terminus moves down a mountain, the terminus is said to be advancing.  When a glacial terminus moves up a mountain, the terminus is said to be retreating.  When a glacial terminus does not move, the terminus is said to be stationary.  How can ice flow uphill?  In fact, the glacial ice within a glacier always flows downhill whether the terminus is advancing, retreating, or stationary.  A retreating terminus simply reveals that the glacier is shrinking in size overall because the overall rate of ablation is greater than the overall rate of accumulation, but the glacial ice still flows downhill in this case.  This can be proven by driving markers into the zone of fracture; while the terminus retreats, the markers still move downhill.  An advancing terminus simply reveals that the glacier is growing in size overall because the overall rate of accumulation is greater than the overall rate of ablation.  Finally, a stationary terminus reveals that the glacier is maintaining the same size overall because the overall rate of accumulation is equal to the overall rate of ablation, but the glacial ice still flows downhill in this case as well.  If a glacial terminus was stationary for several years then suddenly advances by a large amount, it is not because the glacial ice became stuck and then finally became unstuck and flowed downhill.  The glacial ice continued to flow downhill all the years the terminus was stationary.  What actually happened is the overall rate of accumulation was equal to the overall rate of ablation for several years.  Finally, the precipitation happened to be greater one year, causing the overall accumulation to become greater than the overall ablation.  The overall size of the glacier grew, and the terminus advanced.  This is called a glacial surge.

 

There are two forms of glacial weathering (glacial degradation): glacial abrasion and glacial plucking.  Glacial abrasion is the smoothing of rocks as the glacier flows over them.  An alpine glacier may smooth the shapes of entire mountain ranges through this process, turning V-shaped valleys into U-shaped valleys.  A U-shaped valley is more properly called a glacial trough.  A glacial trough that has been drowned by rising sea levels is called a fjord.  Glacial plucking is the ripping of rocks out of surrounding landscapes/environments.  The rocks are then moved by the glacier.

 

As glaciers degrade valleys, they may leave behind a sharp and narrow ridge of mountains.  This is called an aręte, which is a French word meaning not only ridge but sharp knife as well.  Glaciers may also leave behind a single steep mountain after it has degraded the landscapes/environments around it.  This is called a glacial horn.

 

The rocks and sediments eroded by rivers is called fluvial load, and the sediments eroded by wind is called aeolian load.  Unfortunately, the rocks and sediments eroded by glaciers is not called glacial load; it is called glacial drift.  This term derives from the Biblical story of Noah’s flood.  Whenever geomorphologists encountered large boulders that did not match surrounding landscapes/environments, they believed that these boulders drifted in the great flood that the Bible records covered the entire world.  Geomorphologists finally understood that this is not correct; the boulders were moved by glaciers, not a great flood.  Nevertheless, the word drift became stuck in the vocabulary.  Adding the word glacial before the word drift helps to make this term at least half correct.  To summarize, the rocks and sediments that glaciers erode is called glacial drift.  Large boulders that do not match surrounding landscapes/environments are called glacial erratics.

 

We now discuss glacial aggradation.  Glacial till is rocks and sediments that are directly deposited by a glacier.  Since glaciers are strong enough to erode large rocks as well as small sediments, glacial till is more heterogeneous (poorly sorted).  When the glacier melts, the meltwater itself carries sediments and deposits them elsewhere.  Stratified drift is sediments that are deposited by this glacial meltwater.  We may argue that glacial meltwater is simply running water and therefore should be considered a fluvial process.  This is precisely why stratified drift is also called glaciofluvial sediment.  Since glacial meltwater is too weak to erode large rocks, only small sediments are eroded by glacial meltwater.  For this reason, stratified drift is more homogenous (well sorted).

 

A moraine is a layer or ridge of sediment that is either drift being eroded by a glacier or till that has been deposited by a glacier.  There are several different types of moraines.  Lateral moraines are along the edges of glaciers.  Medial moraines are down the middle of glaciers and result from the merging of two lateral moraines.  End moraines are deposited by stationary termini of glaciers, while ground moraines are deposited by retreating termini of glaciers.

 

After a glacier melts, a lake may be all that is left of the glacier.  This is a tarn.  A string of tarns is called paternoster lakes, since they appeared to be a string of rosary beads to monks who saw them.  The word paternoster is Latin for “Our Father” which is one of the prayers recited when praying with rosary beads.  After a glacier melts, all that is left of the head of the glacier is an amphitheater-shaped excavation at the top of the mountain.  This is called a cirque.

 

 

 

Links

 

New Jersey Institute of Technology

College of Science and Liberal Arts at NJIT

Department of Physics at CSLA at NJIT

Libarid A. Maljian at web.njit.edu

Libarid A. Maljian at the Department of Physics at CSLA at NJIT

 

 

 

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