Geomorphology glacier Chapter

1. Geomorphology is concerned with the shaping of landforms, through such
processes as subsidence and uplift, and with the classification and study of such
landforms as mountains, volcanoes, and islands.
An Evolving Area of Study
Geomorphology is an area of geology concerned with the study of landforms, with
the forces and processes that have shaped them, and with the description and
classification of various physical features on Earth. The term, which comes from
the Greek words geo, or "Earth," and morph, meaning "form," was coined in 1893
by the American geologist William Morris Davis (1850-1934), who is considered
the father of geomorphology.
During Davis's time, geomorphology was concerned primarily with classifying
different structures on Earth's surface, examples of which include mountains and
islands, discussed later in this essay. This view of geomorphology as an essentially
descriptive, past-oriented area of study closely aligned with historical geology
prevailed throughout the late nineteenth and early twentieth centuries.
By the mid-twentieth century, however, the concept of geomorphology inherited
from Davis had fallen into disfavor, to be replaced by a paradigm, or model,
oriented toward physical rather than historical geology. (These two principal
branches of geology are concerned, in the first instance, with Earth's past and the
processes that shaped it and, in the second instance, with Earth's current physical
features and the processes that continue to shape it.)

2. • Rethinking Geomorphology
• As reconceived in the 1950s and thereafter, geomorphology became
an increasingly exact science. As has been typical of many sciences in
their infancy, early geomorphology focused on description rather than
prediction and tended to approach its subject matter in a qualitative
fashion. The term qualitative suggests a comparison between qualities
that are not defined precisely, such as "fast" and "slow" or "warm" and
"cold." On the other hand, a quantitative approach, as has been
implemented for geomorphology from the mid-twentieth century
onward, centers on a comparison between precise quantities—for
instance, 10 lb. (4.5 kg) versus 100 lb. (45 kg) or 50 MPH (80.5 km/h)
versus 120 MPH (193 km/h).
• As part of its shift in focus, geomorphology began to treat Earth's
physical features as systems made up of complex and ongoing
interactions. This view fell into line with a general emphasis on the
systems concept in the study of Earth. (See Earth Systems for more
about the systems concept.) As geomorphology evolved, it became
more interdisciplinary, as we shall see. This, too, was part of an
overall trend in the earth sciences toward an approach that viewed
subjects in broad, cross-disciplinary terms as opposed to a narrow
focus on specific areas of study.

3. • Landforms and Processes
• Two concerns are foremost within the realm of geomorphology, and
these concerns reflect the stages of its history. First, in line with
Davis's original conception of geomorphology as an area of science
devoted to classifying and describing natural features, there is its
concern with topography. The latter may be defined as the
configuration of Earth's surface, including its relief (elevation and
other in equalities) as well as the position of physical features.
• These physical features are called landforms, examples of which
include mountains, plateaus, and valleys. Geomorphology always has
involved classification, and early scientists working in this
subdiscipline addressed the classification of landforms. Other systems
of classification, however, are not so concerned with cataloging
topographical features themselves as with differentiating the processes
that shaped them. This brings us to the other area of interest in
geomorphology: the study of how landforms came into being.
• Shaping the Earth
• Among the processes that drive the shaping of landforms is plate
tectonics, or the shifting of large, movable segments of lithosphere
(the crust and upper layer of Earth's mantle). Plate tectonics is
discussed in detail within its own essay and more briefly in other areas
throughout this book, as befits its status as one of the key areas of
study in the earth sciences.

4. • Other processes also shape landforms. Included among these processes
are weathering, the breakdown of rocks and minerals at or near the
surface of Earth due to physical or chemical processes; erosion, the
movement of soil and rock due to forces produced by water, wind,
glaciers, gravity, and other influences; and mass wasting or mass
movement, the transfer of earth material, by processes that include flow,
slide, fall, and creep, down slopes. Also of interest are fluvial and eolian
processes (those that result from water flow and wind, respectively) as
well as others related to glaciers and coastal formations.
• Human activity also can play a significant role in shaping Earth. This
effect may be direct, as when the construction of cities, the building of
dams, or the excavation of mines alters the landscape. On the other hand,
it can be indirect. In the latter instance, human activity in the biosphere
exerts an impact, as when the clearing of forest land or the misuse of crop
land results in the formation of a dust bowl.
• Interdisciplinary Studies
• As noted earlier, geomorphology is characteristic of the earth sciences as
a whole in its emphasis on an interdisciplinary approach. As is true of
earth scientists in general, those studying landforms and the processes
that shape them do not work simply in one specialty. Among the areas of
interest in geomorphology are, for example, deep-sea geomorphology,
which draws on oceanography, and planetary geomorphology, the study
of landscapes on other planets.

5. • When studying coastal geomorphology, a geologist may draw on realms as diverse
as fluid mechanics (an area of physics that studies the behavior of gases and
liquids at rest and in motion) and sedimentology. The investigation of such
processes as erosion and mass wasting calls on knowledge in the atmospheric
sciences as well as the physics and chemistry of soil. It is almost inevitable that a
geomorphologic researcher will draw on geophysics as well as on such
subspecialties as volcanology. These studies may go beyond the "hard sciences,"
bringing in such social sciences as geography.
• Real-Life Applications
• Subsidence
• Subsidence refers to the process of subsiding (settling or descending), on the part
of either an air column or the solid earth, or, in the case of solid earth, to the
resulting formation or depression. Subsidence in the atmosphere is discussed
briefly in the entry Convection. Subsidence that occurs in the solid earth, known
as geologic subsidence, is the settling or sinking by a body of rock or sediment.
(The latter can be defined as material deposited at or near Earth's surface from a
number of sources, most notably preexisting rock.)
• As noted earlier, many geomorphologic processes can be caused either by nature
or by human beings. An example of natural subsidence takes place in the
aftermath of an earthquake, during which large areas of solid earth may simply
drop by several feet. Another example can be observed at the top of a volcano
some time after it has erupted, when it has expelled much of its material (i.e.,
magma) and, as a result, has collapsed.

6. • Man-Made Subsidence
• Man-made subsidence often ensues from the removal of groundwater or
fossil fuels, such as petroleum or coal. Groundwater removal can be
perfectly safe, assuming the area experiences sufficient rainfall to replace, or
recharge, the lost water. If recharging does not occur in the necessary
proportions, however, the result will be the eventual collapse of the aquifer,
a layer of rock that holds groundwater.
• In so-called room-and-pillar coal mining, pillars, or vertical columns, of coal
are left standing, while the areas around them are extracted. This method
maintains the ceiling of the "room" that has been mined of its coal. After the
mine is abandoned, however, the pillar eventually may experience so much
stress that it breaks, leading to the collapse of the mined room. As when the
ceiling of a cave collapses, the subsidence of a coal mine leaves a visible
depression above ground.
• Uplift
• As its name implies, uplift describes a process and results opposite to those
of subsidence. In uplift the surface of Earth rises, owing either to a decrease
in downward force or to an increase in upward force. One of the most
prominent examples of uplift is seen when plates collide, as when India
careened into the southern edge of the Eurasian landmass some 55 million
years ago. The result has been a string of mountain ranges, including the
Himalayas, Karakoram Range, and Hindu Kush, that contain most of the
world's tallest peaks.

7. • Plates move at exceedingly slow speeds, but their mass is enormous. This
means that their inertia (the tendency of a moving object to keep moving
unless acted upon by an outside force) is likewise gargantuan in scale.
Therefore, when plates collide, though they are moving at a rate equal to
only a few inches a year, they will keep pushing into each other like two
automobiles crumpling in a head-on collision. Whereas a car crash is over
in a matter of seconds, however, the crumpling of continental masses
takes place over hundreds of thousands of years.
• When sea floor collides with sea floor, one of the plates likely will be
pushed under by the other one, and, likewise, when sea floor collides
with continental crust, the latter will push the sea floor under. (See Plate
Tectonics for more about oceanic-oceanic and continental-oceanic
collisions.) This results in the formation of volcanic mountains, such as
the Andes of South America or the Cascades of the Pacific Northwest, or
volcanic islands, such as those of Japan, Indonesia, or Alaska's Aleutian
chain.
• Isostatic Compensation
• In many other instances, collision, compression, and extension cause
uplift. On the other hand, as noted, uplift may result from the removal of
a weight. This occurs at the end of an ice age, when glaciers as thick as
1.9 mi. (3 km) melt, gradually removing a vast weight pressing down on
the surface below.

8. • This movement leads to what is called isostatic compensation, or isostatic
rebound, as the crust pushes upward like a seat cushion rising after a person is
longer sitting on it. Scandinavia is still experiencing uplift at a rate of about 0.5
in. (1 cm) per year as the after-effect of glacial melting from the last ice age. The
latter ended some 10,000 years ago, but in geologic terms this is equivalent to a
few minutes' time on the human scale.
• Islands
• Geomorphology, as noted earlier, is concerned with landforms, such as mountains
and volcanoes as well as larger ones, including islands and even continents.
Islands present a particularly interesting area of geomorphologic study. In
general, islands have certain specific characteristics in terms of their land
structure and can be analyzed from the standpoint of the geosphere, but particular
islands also have unique ecosystems, requiring an interdisciplinary study that
draws on botany, zoology, and other subjects.
• In addition, there is something about an island that has always appealed to the
human imagination, as evidenced by the many myths, legends, and stories about
islands. Some examples include Homer's Odyssey, in which the hero Odysseus
visits various islands in his long wanderings; Thomas More's Utopia, describing
an idealized island republic; Robinson Crusoe, by Daniel Defoe, in which the
eponymous hero lives for many years on an island with no companion but the
trusty native Friday; Treasure Island, by Robert Louis Stevenson, in which the
island is the focus of a treasure hunt; and Mark Twain's Adventures of
Huckleberry Finn, depicting Jackson Island in the Mississippi River, to which
Huckleberry Finn flees to escape "civilization."

9. • The Islands of Earth
• Earth has literally tens of thousands of islands. Just two archipelagos (island chains),
those that make up the Philippines and Indonesia, include thousands of islands each.
While there are just a few dozen notable islands on Earth, many more dot the planet's
seas and oceans. The largest are these:
• Greenland (Danish, northern Atlantic): 839,999 sq. mi.(2,175,597 sq km)
• New Guinea (divided between Indonesia and Papua New Guinea, western Pacific):
316,615 sq. mi. (820,033 sq km)
• Borneo (divided between Indonesia and Malaysia, western Pacific): 286,914 sq. mi.
(743,107 sq km)
• Madagascar (Malagasy Republic, western Indian Ocean): 226,657 sq. mi. (587,042 sq
km)
• Baffin (Canadian, northern Atlantic): 183,810 sq. mi. (476,068 sq km)
• Sumatra (Indonesian, northeastern Indian Ocean): 182,859 sq. mi. (473,605 sq km)
• The list could go on and on, but it stops at Sumatra because the next-largest island,
Honshu (part of Japan), is less than half as large, at 88,925 sq. mi. (230,316 sq km).
Clearly, not all islands are created equal, and though some are heavily populated or
enjoy the status of independent nations (e.g., Great Britain at number eight or Cuba at
number 15), they are not necessarily the largest. On the other hand, some of the
largest are among the most sparsely populated.
• Of the 32 largest islands in the world, more than a third are in the icy northern
Atlantic and Arctic, with populations that are small or practically nonexistent.
Greenland's population, for instance, was just over 59,000 in 1998, while that of
Baffin Island was about 13,200. On both islands, then, each person has about 14
frozen sq. mi. (22 sq km) to himself or herself, making them among the most sparsely
populated places on Earth.

10. • Continents, Oceans, and Islands
• Australia, of course, is not an island but a continent, a difference that is not related directly
to size. If Australia were an island, it would be by far the largest. Australia is regarded as a
continent, however, because it is one of the principal landmasses of the Indo-Australian
plate, which is among a handful of major continental plates on Earth. Whereas continents
are more or less permanent (though they have experienced considerable rearrangement
over the eons), islands come and go, seldom lasting more than 10 million years. Erosion or
rising sea levels remove islands, while volcanic explosions can create new ones, as when
an eruption off the coast of Iceland resulted in the formation of an island, Surtsey, in 1963.
• Islands are of two types, continental and oceanic. Continental islands are part of
continental shelves (the submerged, sloping ledges of continents) and may be formed in
one of two ways. Rising ocean waters either cover a coastal region, leaving only the tallest
mountains exposed as islands or cut off part of a peninsula, which then becomes an island.
Most of Earth's significant islands are continental and are easily spotted as such, because
they lie at close proximity to continental landmasses. Many other continental islands are
very small, however; examples include the barrier islands that line the East Coast of the
United States. Formed from mainland sand brought to the coast by rivers, these are
technically not continental islands, but they more clearly fit into that category than into the
grouping of oceanic islands.
• Oceanic islands, of which the Hawaiian-Emperor island chain and the Aleutians off the
Alaskan coast are examples, form as a result of volcanic activity on the ocean floor. In
most cases, there is a region of high volcanic activity, called a hot spot, beneath the plates,
which move across the hot spot. This is the situation in Hawaii, and it explains why the
volcanoes on the southern islands are still active while those to the north are not: the
islands themselves are moving north across the hot spot. If two plates converge and one
subducts (see Plate Tectonics for an explanation of this process), a deep trench with a
parallel chain of volcanic islands may develop. Exemplified by the Aleutians, these chains
are called island arcs.

11. • A bay is a body of water that is partly enclosed
by land (and is usually smaller than a gulf).

12. • Geomorphology (from Greek: γῆ, ge, "earth"; μορφή, morfé,
"form"; and λόγος, logos, "study") is the scientific study of
landforms and the processes that shape them.
• Geomorphologists seek to understand why landscapes look the
way they do: to understand landform history and dynamics, and
predict future changes through a combination of field
observation, physical experiment, and numerical modeling.
• Geomorphology is practiced within geography, geology, geodesy,
engineering geology, archaeology, and geotechnical engineering.
• Early studies in geomorphology are the foundation for pedology,
one of two main branches of soil science.
• More recent studies in geomorphology, pioneered and
popularized by Henry Posamentier, integrate seismic
geomorphology and seismic stratigraphy, leveraging both 2D and
3D seismic data to better understand the paleogeographic
distribution of lithologies.

13. • Landforms evolve in response to a combination of natural
and anthropogenic processes.
• The landscape is built up through tectonic uplift and
volcanism.
• Denudation occurs by erosion and mass wasting, which
produces sediment that is transported and deposited
elsewhere within the landscape or off the coast.
• Landscapes are also lowered by subsidence, either due to
tectonics or physical changes in underlying sedimentary
deposits. These processes are each influenced differently
by climate, ecology, and human activity.
• Practical applications of geomorphology include hazard
assessment including landslide prediction and mitigation,
river control and restoration, and coastal protection.

14. History
• Early geomorphology
• Perhaps the earliest one to devise a theory of geomorphology was the
polymath Chinese scientist and statesman Shen Kuo (1031-1095 AD).
• This was based on his observation of marine fossil shells in a
geological stratum of a mountain hundreds of miles from the
Pacific Ocean. Noticing bivalve shells running in a horizontal span
along the cut section of a cliffside, he theorized that the cliff was once
the pre-historic location of a seashore that had shifted hundreds of
miles over the centuries. He inferred that the land was reshaped and
formed by soil erosion of the mountains and by deposition of silt.
• Furthermore, he promoted the theory of gradual climate change over
centuries of time once ancient petrified bamboos were found to be
preserved underground in the dry, northern climate zone of Yanzhou,
which is now modern day Yan'an, Shaanxi province.

15. • Modern geomorphology
• The first use of the word geomorphology was likely to be in the
German language when it appeared in 's 1858 work. Keith Tinkler has
suggested that the word came into general use in English, German and
French after John Wesley Powell and W. J. McGee used it in the
International Geological Conference of 1891.
• An early popular geomorphic model was the geographical cycle or the
cycle of erosion, developed by William Morris Davis between 1884 and
1899. The cycle was inspired by theories of uniformitarianism (the theory
that geologic events are caused by natural processes, many of which are
operating at the present time) which were first formulated by James Hutton
(1726–1797).
• Concerning , the cycle was depicted as a sequence by which a river would
cut a valley more and more deeply, but then erosion of side valleys would
eventually flatten out the terrain again, now at a lower elevation. The cycle
could be started over by uplift of the terrain. The model is today considered
too much of a simplification to be especially useful in practice.
• Walther Penck developed an alternative model in the 1920s, based on ratios
of uplift and erosion, but it was also too weak to explain a variety of
landforms. Grove Karl Gilbert was an important early American
geomorphologist.

16. Contemporary geomorphology
• Current mainstream views in geomorphology hold that the
classical theories developed in the 1960s and before are too
simplistic and need to be complemented by other ideas.
• These ideas include each landscapes uniqueness,
chaotic determinism, multi-path and multi-outcome processes.
• Contemporary geomorphology recognizes that not all landscapes
may have a normative state, nor do they depend entirely on
climate and that not all landscapes are in a steady state
equilibrium, nor that all follow a necessarily geographic cycle.
• This does not mean that these views are totally outdated, but that
they have lost their central position in the geomorphological
debate and are rather seen as special cases that may occur
depending on time and space scales and geographic locations.

17. Processes
• Modern geomorphology focuses on the
quantitative analysis of interconnected
processes, such as the contribution of solar
energy, the rates of steps of the hydrologic
cycle, tectonic plate movement rates from
geophysics to compute the age and expected
fate of landforms and the weathering and
erosion of the land.
• The use of more precise measurement
techniques has also enabled processes like
erosion to be observed directly, rather than
merely surmised from other evidence. Computer
simulation is also valuable for testing that a
particular model yields results with properties
similar to real terrain.
• Primary surface processes responsible for most
topographic features include wind, waves,
weathering, mass wasting, groundwater,
surface water, glaciers, tectonism, and
volcanism.

18. • Fluvial
• Rivers and streams are not only conduits of water, but also
of sediment. The water, as it flows over the channel bed, is
able to mobilize sediment and transport it downstream,
either as bed load, suspended load or dissolved load. The
rate of sediment transport depends on the availability of
sediment itself and on the river's discharge.
• As rivers flow across the landscape, they generally
increase in size, merging with other rivers. The network of
rivers thus formed is a drainage system and is often
dendritic, but may adopt other patterns depending on the
regional topography and underlying geology.

19. • Aeolian processes pertain to
the activity of the winds and
more specifically, to the
winds' ability to shape the
surface of the Earth. Winds
may erode, transport, and
deposit materials, and are
effective agents in regions
with sparse vegetation and a
large supply of
unconsolidated sediments.
Although water is much
more powerful than wind,
aeolian processes are
important in arid
environments such as deserts
.
Wind-eroded alcove near
Moab, Utah
Mesquite Flat Dunes in Death Valley

20. • Mass wasting, also known as slope
movement or mass movement, is
the geomorphic process by which
soil, regolith, and rock move
downslope under the force of
gravity. Types of mass wasting
include creep, slides, flows,
topples, and falls, each with its own
characteristic features, and taking
place over timescales from seconds
to years. Mass wasting occurs on
both terrestrial and submarine
slopes, and has been observed on
Earth, Mars, Venus, and Jupiter's
moon Io.
• Mass wasting may occur at a very
slow rate, particularly in areas that
are very dry or those areas that
receive sufficient rainfall such that
vegetation has stabilized the
surface. It may also occur at very
high speed, such as in rock slides
or landslides, with disastrous
consequences, both immediate and
delayed, e.g., resulting from the
formation of landslide dams.
Example of mass wasting at
Palo Duro Canyon, Texas

21. • Weathering results from chemical dissolution of rock and
from the mechanical wearing of rock by plant roots, ice
expansion, and the abrasive action of sediment. Weathering
provides the source of the sediment transported by fluvial,
glacial, aeolian, or biotic processes.
• Tectonic effects on geomorphology can range from scales of
millions of years to minutes or less. The effects of tectonics
on landscape are heavily dependent on the nature of the
underlying bedrock fabric which more less controls what
kind of local morphology tectonics can shape. Earthquakes
can, in terms of minutes, submerge large extensions creating
new wetlands. Isostatic rebound can account for significant
changes over thousand or hundreds of years, and orogenies
give rise to large mountain chains on a time scale of millions
of years on which other processes act during and after the
orogeny.

22. • Volcanoes: The action of volcanoes tends to
rejuvenize landscapes covering up old landforms
with lava and tephra eliminating things such as
glacial morphology and forcing rivers through
new paths.
• Biological
• The interaction of living organism with landforms
can be of many different forms. In general the
biological influence on landscape is greatest at
zones with temperate and tropical climate and
their boundary zones with other regions. Boundary
zones include subpolar regions, the tree line and
semiarid areas.

23. • The word "Geomorphology" is derived from the Greek words
γη, ge, "earth"; μορφή, morfé, "form"; and λόγος, logos,
"knowledge". A simple definition is "The form of the earth, the
general configuration of its surface, and the changes that take
place in the evolution of land forms.[1] Put another way,
"Geomorphology takes into account the landforms and
geological history of an area, the processes that have shaped the
landscape, and the time period over which these processes
occur. In other words, geomorphology can be used to explain
the complex evolution of the landscape as we see it today."[2]
• Geomorphologists study the processes of weathering and
erosion, sediment transport and deposition, the characterisation
of landforms and the materials making up their composition.[3]
• Fluvial geomorphology, for example, studies how human use
impacts natural settings in a watershed and determines the shape
of river channels. Fluvial geomorphology attempts to predict
what physical changes will occur to a water channel in response
to alterations in watershed conditions; and how changes will
impact human infrastructure and fish habitat.[4]

24. • Aeolian Geomorphology
• Aeolian geomorphology is the study of the effects of wind erosion,
aeolian processes, on the lithosphere. Winds erode, transport, and
deposit materials world wide. Winds have a greater impact on the
lithosphere in areas with sparse vegetation and unconsolidated, or
loose sediments. Water has a much greater impact overall than wind
but eolian processes are very important in arid environments.[5]
• Aeolioan (or Eolian) refers to wind, a word taken from the name of the
Greek god, Æolus, the keeper of the winds (Latin, from the Greek
Aiolos αιολος). The word itself in ancient Greek literally means rapid
or changeable, quick moving or nimble.[6] [7]
• Wind erosion, or deflation, is created by eddying action that picks up
loose, fine grains of material, exposing surfaces and carrying loose
material away, depositing it over varying distances. In conjunction
with deflation, wind also wears down surfaces by grinding action,
abrasion, and literally sand blasting solid surfaces with wind born
particles. Areas subjected to deflation are termed aeolian deflation
zones.[5]
• Aeolian landforms
• Deflation and abrasion form deflation basins, also called blowouts,
which are hollows formed by aeolian processes. Although generally
small, they may be up to several kilometers in diameter.

25. • Abrasion by particles carried in the wind create grooves or small depressions in solid
surfaces. Ventifacts are characteristic of wind abrasion. Ventifacts are rocks which have
been cut, grooved, pitted and polished by abrasion,
• Larger sculpted landforms known as yardangs, are formations that have been streamlined
by desert winds. They may be up to tens of meters high and kilometers long. Some of the
largest and highest are the yardangs of the Lut Desert of Iran with almost 100 meters of
relief (height above the surrounding land). One theory of the Sphinx of Egypt is that it
was originally a yardang later modified by human sculpting.
• Deflation exposes a sheet-like surface of rock fragments, desert pavement, that remains
after wind and water have removed the loose particulate matter. Nearly half of the
Earth's desert surfaces are stony deflation zones. The remaining rock mantle, or desert
pavement, protects the underlying material from further deflation.
• After extensive deflation and abrasion, desert or rock varnish remains on the surface of
rocks in aeolian zones. Manganese, iron oxides, hydroxides, and clay minerals form
most varnishes which appear as a dark shiny stain. [5]
• Aeolian transportation
• Winds transport solid particulate matter in three ways, suspension, saltation, and creep.
• suspension
• Commonly surface winds may suspend particulate matter less than 0.2 millimeters in
diameter and carry it aloft as dust or haze in the atmosphere for indefinite periods.
• saltation
• Saltation moves small particles downwind, in the direction of the wind, in a series of
short hops or skips. This process usually only lifts sand sized particulate matter up to one
centimetre and carries it about one-half to one-third the speed of the wind. Saltating
grains strike other grains which continue the process.
• creep
• Saltating grains also strike grains that are too heavy to hop, but can be knocked forward,
slowly creeping as they are pushed by saltating grains. Approximately twenty-five
percent of grain movement in a desert is through the creeping process

26. • Aeolian turbidity currents
• Turbidity currents, or dust storms are created when the air is cooled
significantly, by rain for example. Cooler air is denser and sinks
toward the desert surface where it is deflected forward, sweeping up
surface debris, in turn creating turbulence as a dust storm. Most of the
dust is in the form of silt-size particles. Windblown silt is deposited
over extensive distances. These deposits are known as loess
(pronounced ‘lers’). The thickest known deposit of loess on the Loess
Plateau in China, is 335 meters. Elsewhere, for example Europe and in
the Americas, loess deposits are generally 20 to 30 meters thick.
• Whirlwinds
• Small whirlwinds, also known as dust devils, typically occur in arid
areas. Theoretically they are caused by intense local heating of air
which then rises and results in highly localised instabilities. Small
whirlwinds may be as much as one kilometer high. [5]
• Aeolian deposition
• Deposits of sand form sand sheets, ripples and dunes.
• sand sheets
• Sheets are flattened areas of sand that are too large to be carried by
saltation and form an estimated forty percent of aeolian surface
deposits. Sheets may be covered by ripples or dunes.

27. • ripples
• Winds form surface ripples with long axes perpendicular to the wind
direction, with one side of a ripple to the wind. The distance between
the crest of each ripple is the average length of jumps that sand grains
make during saltation. The coarsest materials are collected at the crest
of the ripple.
• dunes
• Windblown sediments accumulate and also form mounds or ridges
called dunes. These dunes have an upwind and a downwind side and
are longitudinal as are ripples. The upwind side (facing the wind) is
much less steep than the down wind side (the lee slope) which forms a
slip-face. The coarsest materials are generally in the troughs between
the dunes. This distinguishes dunes from small ripples where the
coarsest materials are collected on the ridge.
• Dunes move down wind through a series of small avalanches. Wind-
blown material moves up the windward side of a dune by saltation or
creep. As the materials accumulate on the ridge of a dune the build-up
exceeds the angle of repose and small avalanches of sand slid down
the slip-face. In this way the dune slowly moves down wind. [5]

28. Fundamental concepts in Geomorphology
• Concept 1
• “The same physical processes and laws that operate today,
operated throughout geological time, although not
necessarily always with the same intensity as now.”
• The present concept is fundamental principle of modern
geology which is very often popularly known as “principle
of uniformitanism” which was first postulated by
renowened scottish geologist, James Hutton, in 1785. It
may be pointed out that Hutton’s original concept was a bit
different from the concept stated above. He stated that
“geological processes were active with same intensity
during each period of geological time” and thus he
postulated another principle on this concept-”the present is
key to the past” and “novestige of a beginning and no
prospect of an end.”

31. • His concept that physical processes were always active with same intensity
throughout geological periods is erroneous and confusing. For example,
glaciers were more active during Carboniferous and Pleistocene periods than
other processes. At the same time, they were more active than the present
glaciers. The temporal variations in the magnitude of operation of processes
are because of climate changes. For example, the fossils of coal found in great
Britain are indicative of vegetation community of equatorial climate, which
forcefully proves that Great Britain, which enjoys humid temperate climate at
present, was characterised by hot and humid equatorial climate during
Carboniferous period when the present-day tropical areas were dominated by
glacial climate.
• It is obvious that geomorphic and tectonic processes were active in all the
geological periods and their mode of operation was the same as today but the
intensity of erosional and depositional works differed temporally.
• The processes (mainly endogenetic) which affect the earth’s crust act in a
cyclic manner. Hutton believed in orderliness of nature i.e. the nature evolves
in orderly course. According to him, the nature is systematic, orderly,
coherent and reasonale –destruction leads to construction while construction
results into destruction. Denudation of uplands (destruction) leads to
sedimentation in

32. • lowlying areas giving birth to alluvial plains (construction). Continuous
sedimentation leads to subsidence of ground surface. The nature has inbuilt
self regulatory mechanism known as homeostatis mechanism which acts in
such manner that any change effected by natural factors (whether endogenetic
or exogenetic) is suitably compensated by changes in other components of the
natural system.
• Hutton was the first scientist who postulated the “concept of cyclic nature of
earth’s history.” All major geological activities are repeated in cyclic manner.
There have been four major periods of mountain building –precambrian,
caledonian, hercynian and tertiary periods of mountain building. Similarly,
glacial periods during Pleistocene ice age were separated by interglacial
period.
• But it is difficult to find out as to when a particular geological processes
began to work and it is equally difficult to predict as to when a particular
process would cease to work. Based on this Hutton postulated the concept- “
no vestige of beginning: no prospect of an end.”
• Denudation chronology-Peninsular India has passed through several phases of
cyclic development e.g. Dharwar landscape cycle--Cuddapah-vindhyan
landscape cycle—Cambrian landscape cycle—Cenozoic landscape cycle etc.

33. • Concept 2
• “Geologic structure is a dominant control factor in the evolution of landforms
and is reflected in them.”
• The above concept demonstrates imposing influence of geological structure
on primary and secondary landforms (produced by exogenetic-denudational
process). W.M. Davis included structure in his trio namely srtucture, process,
and time, as important controlling factors of landscape development through
his postulate that landscape is a function of structure, process and time but he
game more importance to “time”. Even the modern geomorphologists like J.
T. Hack, R. J. Chorley, S. Schumm, D. E. Sugden, etc. have clearly outlined
influences of geological structure on landforms. “Exposed rocks are
immediately acted upon by exogenetic weathering and erosional processes to
form secondary landforms, which reflected geologic controls at both global
and local scales.”
• 1. Lithology or nature of rocks
• Igneous topography
• Sedimentary landforms
• Metamorphic landforms

34. • 2. Arrangement of rocks
• Folded structure and landforms
• Faulted structure and landforms
• Domed structure
• Uniclinal/Homoclinal structure
• Horizontal structure and landforms
• 3. rock characteristics
• Rock joints, Permeability, rock hardness.

35. • Granite is uplifted to
the surface during a
mountain-building
event. During the
mountain building process
, the overlying rock is
eroded as the granite is
uplifted, and the
pressure on the granite
reduced. The granite
expands and forms
fractures or sheet joints
parallel to the surface.
The granite then erodes
in concentric layers
(similar to how an
onion peels) forming
rounded masses called
exfoliation domes.

36. • The term badlands is also apt: badlands contain steep slopes, loose dry soil, slick
clay, and deep sand, all of which impede travel and other uses. Badlands form in
semi-arid or arid regions with infrequent but intense rain-showers, sparse
vegetation, and soft sediments: a recipe for massive erosion.

37. • Energy of Erosion
• The energy for erosion comes from several sources. Mountain
building creates a disequilibrium within the Earth's landscape
because of the creation of relief. Gravity acts to vertically
move materials of higher relief to lower elevations to produce
an equilibrium. Gravity also acts on the mediums of erosion
to cause them to flow to base level.
• Solar radiation and its influence on atmospheric processes is
another source of energy for erosion. Rainwater has a
kinetic energy imparted to it when it falls from the
atmosphere. Snow has potential energy when it is deposited
in higher elevations. This potential energy can be converted
into the energy of motion when the snow is converted into
flowing glacial ice. Likewise, the motion of air because of
differences in atmospheric pressure can erode surface material
when velocities are high enough to cause particle entrainment
.

38. • The Erosion Sequence
• Erosion can be seen as a sequence of three events: detachment,
entrainment, and transport. These three processes are often
closely related and sometimes not easy distinguished between each
other. A single particle may undergo detachment, entrainment, and
transport many times.
• Detachment
• Erosion begins with the detachment of a particle from
surrounding material. Sometimes detachment requires the breaking
of bonds which hold particles together. Many different types of
bonds exist each with different levels of particle cohesion. Some of
the strongest bonds exist between the particles found within
igneous rocks. In these materials, bonds are derived from the
growth of mineral crystals during cooling. In sedimentary rocks,
bonds are weaker and are mainly caused by the cementing effect of
compounds such as iron oxides, silica, or calcium. The particles
found in soils are held together by even weaker bonds which result
from the cohesion effects of water and the electro-chemical bonds
found in clay and particles of organic matter.

39. • Physical, chemical, and biological weathering act to weaken the
particle bonds found in rock materials. As a result, weathered
materials are normally more susceptible than unaltered rock to the
forces of detachment. The agents of erosion can also exert their
own forces of detachment upon the surface rocks and soil through
the following mechanisms:
• Plucking: ice freezes onto the surface, particularly in cracks and
crevices, and pulls fragments out from the surface of the rock.
• Cavitation: intense erosion due to the surface collapse of air
bubbles found in rapid flows of water. In the implosion of the
bubble, a micro-jet of water is created that travels with high
speeds and great pressure producing extreme stress on a very
small area of a surface. Cavitation only occurs when water has a
very high velocity, and therefore its effects in nature are limited
to phenomenon like high waterfalls.

40. • Raindrop impact: the force of a raindrop falling onto
a soil or weathered rock surface is often sufficient to
break weaker particle bonds. The amount of force
exerted by a raindrop is a function of the terminal
velocity and mass of the raindrop.
• Abrasion: the excavation of surface particles by
material carried by the erosion agent. The effectiveness
of this process is related to the velocity of the moving
particles, their mass, and their concentration at the
eroding surface. Abrasion is very active in glaciers
where the particles are firmly held by ice. Abrasion can
also occur from the particles held in the erosional
mediums of wind and water.

41. • Entrainment
• Entrainment is the process of particle lifting by the agent of
erosion. In many circumstances, it is hard to distinguish
between entrainment and detachment. There are several forces
that provide particles with a resistance to this process. The most
important force is frictional resistance. Frictional resistance
develops from the interaction between the particle to its
surroundings. A number of factors increase frictional resistance,
including: gravity, particle slope angle relative to the flow
direction of eroding medium, particle mass, and surface
roughness.
• Entrainment also has to overcome the resistance that occurs
because of particle cohesive bonds. These bonds are weakened
by weathering or forces created by the erosion agent (abrasion,
plucking, raindrop impact, and cavitation).

42. • Entrainment Forces
• The main force reponsible for entrainment is fluid drag. The
strength of fluid drag varies with the mass of the eroding medium
(water is 9000 times more dense than air) and its velocity. Fluid
drag causes the particle to move because of horizontal force and
vertical lift. Within a medium of erosion, both of these forces are
controlled by velocity. Horizontal force occurs from the push of
the agent against the particle. If this push is sufficient to overcome
friction and the resistance of cohesive bonds, the particle moves
horizontally.
• The vertical lift is produced by turbulence or eddies within the
flow that push the particle upward. Once the particle is lifted the
only force resisting its transport is gravity as the forces of friction,
slope angle, and cohesion are now non-existent. The particle can
also be transported at velocities lower than the entrainment
velocities because of the reduction in forces acting on it.

43. • The critical entrainment velocity curve suggests that particles below a
certain size are just as resistant to entrainment as particles with larger sizes
and masses (Figure 10w-2). Fine silt and clay particles tend to have higher
resistance to entrainment because of the strong cohesive bonds between
particles. These forces are far stronger than the forces of friction and gravity.

44. • Transport
• Once a particle is entrained, it tends to move as long as the velocity
of the medium is high enough to transport the particle horizontally.
Within the medium, transport can occur in four different ways:
• Suspension is where the particles are carried by the medium
without touching the surface of their origin. This can occur in air,
water, and ice.
• Saltation is where the particle moves from the surface to the
medium in quick continuous repeated cycles. The action of
returning to the surface usually has enough force to cause the
entrainment of new particles. This process is only active in air and
water.
• Traction is the movement of particles by rolling, sliding, and
shuffling along the eroded surface. This occurs in all erosional
mediums.
• Solution is a transport mechanism that occurs only in aqueous
environments. Solution involves the eroded material being dissolve
and carried along in water as individual ions.
• Particle weight, size, shape, surface configuration, and medium
type are the main factors that determine which of these processes
operate.

45. • Deposition
• The erosional transport of material through the landscape is rarely
continuous. Instead, we find that particles may undergo repeated
cycles of entrainment, transport, and deposition. Transport depends
on an appropriate balance of forces within the transporting medium. A
reduction in the velocity of the medium, or an increase in the
resistance of the particles may upset this balance and cause deposition.
Reductions in competence can occur in a variety of ways. Velocity can
be reduced locally by the sheltering effect of large rocks, hills, stands
of vegetation or other obstructions. Normally, competence changes
occur because of large scale reductions in the velocity of flowing
medium. For wind, reductions in velocity can be related to variations
in spatial heating and cooling which create pressure gradients and
wind. In water, lower velocities can be caused by reductions in
discharge or a change in the grade of the stream. Glacial flows of ice
can become slower if precipitation input is reduced or when the ice
encounters melting. Deposition can also be caused by particle
precipitation and flocculation. Both of these processes are active
only in water. Precipitation is a process where dissolved ions become
solid because of changes in the temperature or chemistry of the water.
Flocculation is a chemical process where salt causes the aggregation
of minute clay particles into larger masses that are too heavy to remain
suspended.

46. Glacial
landforms are
those created
by the action
of glaciers.
Most of
today's glacial
landforms
were created
by the
movement of
large
ice sheets
during the
Quaternary glaciations
.

47. Glacier: The moving ice mass downslope under the impact of gravity is called
glacier (a Flowing Stream of Ice)
Mountain
Continental (Greenland, Antarctica)
Snowfall vs Melting & Evaporation (Ablation)

48. Glaciers are formed due to accumulation of ice above snow-line under
extreme cold climate. Snowline is generally defined as a zone between
permanent and seasonal snow. Snowline denotes the height above which
there is permanent snow cover and thus it corresponds to the level where
average temperature is always below freezing point during the warmest
month of the year.
The areas of accumulation of huge volume of ice are called snowfield
which generate glaciers of different dimensions.
The glaciers grow by gradual transformation of snow into granular snow,
then into firn or neve and finally into solid glacial ice.
Snow is a fluffy mass of loosely packed snowflakes of very low density
having an open feather-like appearance.
Semi-compacted snow due to the weight of overlying snow is transformed
into granular snow of denser form. Such granular snow is called firn or
neve.
It is intermediate between snow and glacial ice.
Further compaction of granular snow produces pure solid glacial ice.

49. • Glaciers, while geographically restricted, are effective agents of landscape
change. The gradual movement of ice down a valley causes abrasion and
plucking of the underlying rock. Abrasion produces fine sediment, termed
glacial flour.
• The debris transported by the glacier, when the glacier recedes, is termed a
moraine. Glacial erosion is responsible for U-shaped valleys, as opposed to
the V-shaped valleys of fluvial origin.

50. Glacial Landforms
Mountain Glacier
Landforms

51. Continental Glacier
Landforms

52. • Erosional work of glaciers:
• The erosional work of the glaciers is accomplished
through the mechanisms of abrasion, plucking and
polishishing.
• Pure ice mass is not geomorphologically active but when
coarse debris is carried by the glaciers at its base it
becomes active agent of erosion.
• The glacier erodes its bed and side walls with the help of
tools of erosion (coarse debris) through the mechanism of
abrasion. The mechanical wearing away of a rock by
friction, rubbing, scraping or grinding.
• Large particles of well jointed rocks are detached by
moving glacial ice and this is called plucking.

53. • U- shaped Valleys: The cross valleys or glacial troughs
o mountain glaciers is U shaped which is characterised
by steep valley walls with concave slope and broad and
flat valley floor.
• Hanging Valleys: The valleys of tributery glaciers
which join the main glacial valleys of much greater
depth are called hanging valleys.
• Cirques: The armchar-shaped cirque or corie is a horse
shoe-shaped, steep-walled depression representing a
glaciated valley head. It is excavated by ice plucking
and frost wedging (due to expansion of water as it
freezes).
• Arete: A narrow, sharp ridge separating two adjacent
glacial valleys.
• Horn: A sharp peak formed at the intersection of the
headwalls of three or more cirques.

56. • Transportation and depositional works of glaciers
• The rock debris carried by the glaciers are collectively
called glacial drifts (glacial sediments of varying sizes).
The glacial debris is divided into 3 types on the basis of
location e.g. (1) englacial debris which is transported
within the glacier. (2) supraglacial debris which exists
on the surface of the glacier and (3) subglacial debris
which is found at the base of the glacier.
• Glacial sediments are transported along the sides, floor
and snout of the glacier (end of the glacier). The debris
falling on to the surface of a glacier is transported
downslope along with the moving ice mass. The
materials derived from the bed by subglacial erosion are
transported by touching the bottom.

57. • Depositional landforms
• Depositional landforms formed due to setling down of
glacial drifts (glacial sediments of varying sizes) include
moraines or morainic ridges and drumlins.
• Moraines: Moraines are ridge like depositional features of
glacial tills. They are long but narrow ridges with height
more than 30 m. Moraines are generally divided into 4
main categories on the basis of locational aspect of glacial
deposits.
• 1. end or terminal or recessional moraines (at the snouts of
glaciers after ablation of ice)
• 2. lateral moraines (parallel ridges of till on either side of a
glacier-along the margin)
• 3. medial moraines (along the internal margins of two
glaciers at their confluence)
• 4. ground moraines (at the floor of glacial valleys).

58. • Drumlins: The swarms of rounded hummocks resulting from the
deposition of glacial till are called drumlins. They look like an
inverted boat or spoon. Drumlins are elliptical hills and steeper slope
with an elongate down glacier tail.
• Glacio-fluvial deposits and landforms:
• The snout of a glacier starts melting due to increase in temperature
when it descends below snow-line. The process of melting of a
glacier is called ablation. Melt water escapes through numerous but
small and temporary streams. These streams still carry some ice.
Thus, the deposition of sediments after the ablation of a glacier is
called glacio-fluvial deposits and the landforms resulting from such
deposit are called glacio-fluvial landforms. The sediments are
deposited in the form of low alluvial fans (if deposited on land) or
deltas (if deposited on standing water).
• The fans spread out and coalesce into plains called as outwash
plains.
• The glacio-fluvial landforms include eskers, kames, kame terrace,
kettle, kettle holes, outwash plains etc.
•

60. • Eskers: Eskers are long, narrow and sinuous ridges of sands and
gravels and are situated in the middle of ground moraines. The
sides of eskers are very steep. They vary in height and width
ranging from a few meters to tens of meters and extend for
kilometers in length parallel to the direction in which ice moved
previously.
• Kames: Kames are small hills or irregular mounds of bedded
sands and gravels which are deposited by melt water near or at
the edge of the retreating ice sheet.
• Outwash: The melt water caused due to ablation of a glacier at its
snout descends through the terminal moraine and spreads like
sheet water. These spreading water erodes the terminal moraines
and deposits the eroded sediments in front of the terminal
moraines and thus forms a plain which is called outwash plain.
• Kettles and Hummocks: Kettles are depressions in the outwash
plains. Kettles are formed due to melting of large blocks of ice.
Large kettles are dotted with numerous low mounds which are
called hummocks.