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216 Cards in this Set

  • Front
  • Back
What is the Pleistocene?
Consequently, when referring to the Ice Age, capitalized, we usually mean this most recent ice age, which is the main feature of the geologic epoch known as the Pleistocene, a period that began about 2.5 million years ago and ended about 10,000 years ago.
??
The landforms resulting from continental glaciation conform quite closely to the clearly defined limits of continental ice sheets during the Pleistocene, and landforms from mountain glaciation can be found in almost all high mountain areas—even in the tropics.
??
glaciers are clear-cut examples of open systems with inputs and outputs of both material and energy
What are the two main types of glaciers?
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How is the extent of glaciers today different from what it was at the peak of the Pleistocene glaciations?
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How do glaciers form and move?
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How do glaciers erode, transport, and deposit rock?
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What landforms are produced by the erosion, deposition, and meltwater of continental ice sheets?
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What landforms are produced by the erosion and deposition of mountain glaciers?
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How can glacial conditions affect the landscape beyond the margin of the ice?
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What are some of the likely causes of the Pleistocene glaciations?
??
The Impact of Glaciers on the Landscape.
• Snowpack over years turns to ice
• Ice mass motion under gravity grinds anything in its path
• Glaciation increases erosion rate on a mountain by at least 10 times to an unglaciated mountain
• Modifies flat landscapes as well
Explain the Impact of Glaciers on the Landscape?
Wherever glaciers have developed, they have had a significant impact on the landscape simply because moving ice grinds away almost anything in its path: most soil is carried away, and bedrock is polished, scraped, gouged, plucked, and abraded.
Moreover, the rock that is picked up is eventually deposited in a new location, further changing the shape of the terrain.
In short, preglacial topography is significantly reshaped.
Explain the Impact of Glaciers on the Landscape?
Perhaps 7% of all contemporary erosion and transportation of rock debris on the continents is accomplished by glaciers.
This is a small amount in comparison with fluvial erosion, but considering how small a land area is covered by glacial ice today, it is clear that glaciers make a significant contribution to continental denudation.
Explain the Impact of Glaciers on the Landscape?
Glaciation modifies flat landscapes greatly, with the result that postglacial slope, drainage, and surficial material are likely to be totally different from what they were before the glacier passed by.
In mountainous areas, the metamorphosis of the landscape may be less complete, but the topography is often deepened and steepened, and in many places rounded, by glacial action.
Types of Glaciers.
• Continental Ice Sheets
– Exist in non mountainous areas
– Antarctica and Greenland only two

• Mountain Glaciers
– Highland Icefields: ice sheets that submerge most underlying topography; valley and piedmont glaciers
– Alpine glaciers: develop individually instead of part of ice field, cirque glaciers
A Glacier?
A glacier is more than a block of ice filling up a mountain valley or resting on a continental plain; it is a finely tuned environmental system with a delicately balanced nourishment budget.
Although glacial ice behaves in similar fashion wherever it accumulates, its pattern of movement and its effect on topographic shaping can vary considerably depending on the quantity of ice involved and particularly on the environment.
Behavior of Glacial Ice?
Although glacial ice behaves in similar fashion wherever it accumulates, its pattern of movement and its effect on topographic shaping can vary considerably depending on the quantity of ice involved and particularly on the environment.
Different Types of Glaciers?
1. Mountain Glaciers
2. Continental Ice Sheets
Mountain Glaciers?
In a few high-mountain areas today, ice accumulates in an unconfined sheet that may cover a few hundred or few thousand square kilometers, submerging all the underlying topography except perhaps for some protruding pinnacles called nunataks.
-Highland Icefields
- Alpine Glaciers
- Piedmont Glacier
What are Highland Icefields?
Ice sheets that submerge most underlying topography; valley and piedmont glaciers
Their outlets are often tongues of ice that travel down valleys in the mountains and so are called valley glaciers
What is a Piedmont Glacier?
If the leading edge of a valley glacier reaches a flat area and so escapes from the confines of its valley walls, it is called a piedmont glacier
What are Alpine Glaciers?
Sometimes the term alpine glacier is used to describe glaciers that develop individually, high in the mountains rather than as part of a broad icefield, usually at the heads of valleys.

(Develop individually instead of part of ice field, cirque glaciers)

Very small alpine glaciers confined to the basins where they originate are called cirque glaciers.
Normally, however, alpine glaciers spill out of their originating basins and flow downvalley as long, narrow valley glaciers.
Occasionally they extend to the mouth of the valley and become piedmont glaciers.
What are Cirque Glaciers?
Very small alpine glaciers confined to the basins where they originate are called cirque glaciers (because the basin is called a cirque)
Continental Ice Sheets?
– Exist in non mountainous areas
– Antarctica and Greenland only two
What are Continental Ice Sheets?
Glaciers that form in nonmountainous areas of the continents are called continental ice sheets.

Because of their immense size, ice sheets have been the most significant agents of glaciation across the land surface.

Only two Continental Ice Sheets exist today:
One in Antarctica and one in Greenland
Where are the Only Two Remaining Continental Ice Sheets Located?
Antarctica and Greenland
Antarctica and Greenland
An Ice Sheet.
The ice in an ice sheet accumulates to great depths in the interior of the sheet but is much thinner at the outer edges.
What are Outlet Glaciers?
Around the margin of the ice sheet, some long tongues of ice, called outlet glaciers, extend between rimming hills to the sea.
What is an Ice Shelf?
In other places, the ice reaches the ocean along a massive front, where it sometimes projects out over the sea as an ice shelf
What are Icebergs?
Great chunks of ice frequently break off, both from the ice shelves and from the ends of outlet glaciers, fall into the sea, and float away. These huge floating ice masses are icebergs.
Types of Mountain Glaciers:
Valley and piedmont glaciers can originate in a highland icefield, or when an alpine glacier overflows its cirque and flows downvalley. Nunataks are pinnacles rising above the ice of a highland icefield.
Valley and piedmont glaciers can originate in a highland icefield, or when an alpine glacier overflows its cirque and flows downvalley. Nunataks are pinnacles rising above the ice of a highland icefield.
LC 19-1?
??
??
When either an ice sheet or an outlet glacier reaches
the ocean, some of the ice may extend out over the water as an ice shelf. Icebergs form when the hanging ice of the shelf breaks off and floats away, a process called calving.
When either an ice sheet or an outlet glacier reaches
the ocean, some of the ice may extend out over the water as an ice shelf. Icebergs form when the hanging ice of the shelf breaks off and floats away, a process called calving.
Glaciations Past and Present.
The amount of glacial ice on Earth’s surface has varied remarkably over the last few million years, with periods of accumulation interspersed with periods of melting and times of ice advance alternating with times of ice retreat.
A great deal of secondary evidence was left behind by the moving and melting ice, and scientists have been remarkably insightful in piecing together the chronology of past glaciations.
Pleistocene Glaciation. (LS)
– Began at least 2.59 million years ago
– Last major ice retreat occurred only 9000 years ago
– Dominant environmental characteristic was refrigeration of high-latitude and high-elevation areas
– Consistent alterations of glacial and interglacial periods
– Wisconsin glacial stage last stage….but the last one?
– At peak, 1/3 of total land covered in ice
– Laurentide ice and the Driftless Area
Pleistocene Glaciation: What is the dominant environmental characteristic of the Pleistocene?
The dominant environmental characteristic of the Pleistocene was the cooling of high latitude and high elevation areas, so that a vast amount of ice accumulated in many places; (Dominant environmental characteristic was refrigeration of high-latitude and high-elevation areas)
Pleistocene Glaciation:
The Pleistocene was not universally icy.
During several lengthy periods, most or all of the ice melted, only to be followed by intervals of ice accumulation.
In broad terms, the Pleistocene consisted of an alternation of glacial periods (times of ice accumulation) and interglacial periods (times of ice retreat).
When did the Pleistocene Epoch (Pleistocene Glaciation) Begin?
Current estimates define the start of the Pleistocene as 2.59 million years ago
The Pleistocene Epoch:
The Pleistocene Epoch occupied almost all of the most recent two and a half million years of Earth’s history.
The End of the Pleistocene Epoch?
The end of the Pleistocene Epoch coincided with the conclusion of what is known in North America as the “Wisconsin” glacial stage, approximately 11,000 years ago.
The Holocene Epoch?
The period since then (the Pleistocene Epoch) is identified as the Holocene Epoch. Conceptually, then, the Holocene is either a postglacial epoch or the latest in a series of interglacial interludes.
What Epoch followed the Pleistocene Epoch? (What is the period since the Pleistocene Epoch?)
The period since then (the Pleistocene Epoch) is identified as the Holocene Epoch. Conceptually, then, the Holocene is either a postglacial epoch or the latest in a series of interglacial interludes.
Extent of Pleistocene Glaciations?
At its maximum Pleistocene extent, ice covered 1/3 of the total land area of Earth
??
The greatest total area of ice-covered land was in North America.
The greatest total area of ice-covered land was in North America.
Laurentide Ice?
The Laurentide ice, which covered most of Canada and a considerable portion of the northeastern United States, was the most extensive Pleistocene ice mass; its area was slightly larger than that of the present glacier covering Antarctica. It extended southward into the United States to approximately the present location of Long Island, the Ohio River, and the Missouri River.
The Driftless Area?
Most of western Canada and much of Alaska were covered by an interconnecting network of smaller glaciers. For reasons we do not fully understand, however, a small area in northwestern Canada as well as extensive portions of northern and western Al...
Most of western Canada and much of Alaska were covered by an interconnecting network of smaller glaciers. For reasons we do not fully understand, however, a small area in northwestern Canada as well as extensive portions of northern and western Alaska were never glaciated during the Pleistocene.

This area, referred to as the Driftless Area, was apparently never completely surrounded by ice; rather, ice encroached first on one side during one glacial advance and then on the other side during a different advance.
LC 19-2?
??
Indirect Effects of Pleistocene Glaciations.
The accumulation of ice and the movement and melting of the resulting glaciers had an enormous effect on topography and drainage. In addition, however, there were several indirect effects of Pleistocene glaciations:
Indirect Effects of Pleistocene Glaciations: Periglacial Processes?
Beyond the outermost extent of ice advance is an area of indefinite size called the periglacial zone, which was never touched by glacial ice but where indirect influence of the ice was felt.
Periglacial Processes. (LS)
• Periglacial Zone—zone where ice never existed but glacial factors affected the landscape such as erosion from ice melt, Solifluction
Periglacial Zone An area of indefinite size beyond the outermost extent of ice advance that was indirectly influenced by glaciation.
• Sea-level changes—buildup of ice on continents led to less drain water on continents and brought about a lowering of sea levels
• Crustal depression—the weight of the ice on the continents caused continents to sink, ice melt allowed for continental rebound
• Pluvial developments—considerable runoff results in increased moisture, leading to increased precipitation and less evaporation. Developed many lakes, including the Great Salt Lake (formed from Lake Bonneville)
What was the Periglacial Zone?
The zone which was never touched by glacial ice but where indirect influence of the ice was felt.

(zone where ice never existed but glacial factors affected the landscape such as erosion from ice melt, solifluction)
What were some of the Most Important Periglacial Processes?
The most important periglacial processes were the erosion and deposition done by the prodigious amounts of meltwater released as the glaciers melted.

Also important were frost weathering caused by the low temperatures in the periglacial zone and the associated solifluction of frozen subsoil
What is Solifluction?
??
??
It is estimated that periglacial conditions extended over more than 20% of Earth’s land area.
Indirect Effects of Pleistocene Glaciations: Sea-level Changes?
(buildup of ice on continents led to less drain water on continents and brought about a lowering of sea levels)

The buildup of ice on the continents meant that less water was available to drain from the continents into the oceans, a condition that resulted in a world wide lowering of sea level during every episode of glacial advance; when the glaciers retreated, sea level would again rise as meltwater returned to the oceans.

The fluctuation in the amount of ocean water between the global sea level in the Pleistocene Epoch and today, caused a significant difference in drainage patterns and topographic development on sea shores and coastal plains.
LC 19-3: Why did sea level fluctuate during the Pleistocene?
??
Indirect Effects of Pleistocene Glaciations: Crustal Depression?
(the weight of the ice on the continents caused continents to sink, ice melt allowed for continental rebound)

The enormous weight of accumulated ice on the continents caused portions of Earth’s crust to sink.

After the ice melted, the crust slowly began to rebound. This isostatic adjustment has not yet been completed, and some portions of Canada and northern Europe are still rising
Isostasy?
the equilibrium that exists between parts of the earth's crust, which behaves as if it consists of blocks floating on the underlying mantle, rising if material (such as an ice cap) is removed and sinking if material is deposited.
Indirect Effects of Pleistocene Glaciations: Pluvial (Increased Rain) Developments?
(considerable runoff results in increased moisture, leading to increased precipitation and less evaporation.)

Developed many lakes, including the Great Salt Lake (formed from Lake Bonneville)

During the Pleistocene glaciations, there was, on almost all areas of the continents, a considerable increase in the amount of moisture available.
This increase was caused by a combination of meltwater runoff, increased precipitation, and decreased evaporation.
A prominent result of these pluvial effects was the creation of many lakes in areas where none had previously existed. Most of these lakes have subsequently been drained or significantly reduced in size, but they have left lasting imprints on the landscape.
What are Pluvial Effects?
Pertaining to rain; often used in connection with a past rainy period.
Pleistocene Lakes?
Created as a result of pluvial effects: Pluvial Effects Developed many lakes, including the Great Salt Lake (formed from Lake Bonneville)
LC 19-4?
??
Contemporary Glaciation. (LS)
– Limited ice cover today (about 10% of total land surface)
– 96% of the total ice cover is Greenland and Antarctica
– Antarctic ice sheet
– Greenland ice sheet
– North American glaciers
Contemporary Glaciation?
In marked contrast to Pleistocene glaciation, the extent of ice covering the continental surfaces today is very limited, (about 10% of total land surface is covered by ice today with more than 96% being in Antarctica and Greenland.)

Something m...
In marked contrast to Pleistocene glaciation, the extent of ice covering the continental surfaces today is very limited, (about 10% of total land surface is covered by ice today with more than 96% being in Antarctica and Greenland.)

Something more than 2/3 of all the world’s freshwater is at this moment frozen into glacial ice.
Contemporary Glaciation: Antarctic Ice Sheet?
• Consists of two unequal sections separated by Transantarctic mountains)
• West Antarctica has a few “dry valleys”

Antarctic Ice is by far the most extensive ice sheet on Earth.
Presently, about 98% of its surface is covered with glacial ice, representing almost 90% of the world’s land ice total.

Physically the continent and its ice sheets can be thought of as consisting of two unequal sections separated by the wide upland belt of the Transantarctic Mountains.

West Antarctica, the smaller of the two sections, is generally mountainous. It contains, however, a few interior valleys that are curiously ice free, called "Dry Valley"

Because winds blast away snow and keep precipitation out, the "Dry Valley" area does not build ice.

The three major parallel valleys contain several large lakes, a number of ponds, and a river that flows for one or two months each year.
What is the "Dry Valley"?
Valleys that are curiously ice free.

Because winds blast away snow and keep precipitation out, the "Dry Valley" area does not build ice.
Greenland Ice Sheet
.
Mountain Glaciers
Other than the two major ice caps, the remainder of the world’s present-day glaciers are concentrated in high mountain areas.
Climate Change and Contemporary Glaciation. (LS)
– Retreating of polar ice sheets
– Shrinking ice caps an indicator of a warming climate
– Antarctic ice shelves breaking
– Higher flow rates of outlet glaciers
Climate Change and Contemporary Glaciation
Global climate change is significantly influencing the extent of contemporary glaciation.

The retreat of the Arctic sea ice pack and the loss of mass of Greenland’s ice sheets is indicative of the higher temperatures experienced in the high latitudes of the Northern Hemisphere. (Retreating of polar ice sheets)

Glaciers are sensitive indicators of environmental change—reflecting variations in both temperature and precipitation.

Antarctic ice shelves breaking
Higher flow rates of outlet glaciers
Shrinking ice caps an indicator of a warming climate
Climate Change and Contemporary Glaciation: The Warming of West Antarctica?
A study showed that West Antarctica has been warming much faster than the continent as a whole. This warming is not only leading to the breakup of Antarctic ice shelves, but to higher flow rates of outlet glaciers as well.
LC 19-5: How is climate change affecting glaciers today?
??
Glacier Formation and Movement. (LS)
• Require balance between accumulation and ablation
• Snow begins as crystallized water vapor
• Compressed to granular form
• More compression causes granules to coalesce, névé/firn
• Further compression results in glacial ice
• Ablation and accumulation zones
Glacier Formation and Movement?
Glacier Formation
Snow falls and ice accumulates in many parts of the world, but glaciers do not always develop from these events. Glaciers require certain circumstances to form and then depend on just the right combination of temperature and moisture to survive. A slight warming or drying trend for a few decades can cause even the most extensive ice sheet to disappear.
The persistence of any glacier depends on the balance between accumulation (addition of ice by incorporation of snow) and ablation (wastage of ice through melting and sublimation).
Explain how a Glacier is formed.
A glacier may begin to develop when there is a net year-to-year accumulation of snow—that is, when over a period of years the amount of snow that falls in a winter is greater than the amount that melts the following summer. The snow that falls the next winter weighs down on the old snow and turns it to ice. After many years of such accumulation, the ice mass begins to move under the pull of gravity—and a glacier is formed.
What is Accumulation?
(addition of ice by incorporation of snow)
What is Ablation?
(wastage of ice through melting and sublimation).
The Persistence of any Glacier Depends on What two things?
(Every glacier can be divided into two portions)
The persistence of any glacier depends on the balance between"
1. Accumulation and
2. Ablation.

Every glacier can be divided into two portions on the basis of the balance between accumulation and ablation
What is Snow?
Snow is not merely frozen water; rather, it is a substance that has crystallized directly from water vapor in the atmosphere and floats to Earth as lacy, hexagonal crystals that are only about 1/10 as dense as liquid water.
What is Névé (Firn)?
Snow granules that have become packed and begin to coalesce due to compression, achieving a density about half as great as that of water
How is Glacial Ice Formed?
As time passes, the further compression of névé results in glacial ice (dense glacial ice absorbs most wave- lengths of visible light, but reflects and scatters blue light)
What is Glacial Ice?
dense glacial ice absorbs most wavelengths of visible light, but reflects and scatters blue light
Changing Snow to Ice.
Snow is changed to ice by compression and coalescence, following a sequence from snowflake to granular snow to névé to glacial ice.
Snow is changed to ice by compression and coalescence, following a sequence from snowflake to granular snow to névé to glacial ice.
??
Every glacier can be divided into two portions on the basis of the balance between accumulation and ablation
Every glacier can be divided into two portions on the basis of the balance between accumulation and ablation
.
.
Cross section through an alpine glacier. The upper portion is an area of net ice accumulation. Below the equilibrium line there is more ablation than accumulation.
What is the Accumulation Zone?
The upper portion is called the accumulation zone because here the amount of new ice from snowfall added each year exceeds the amount lost by melting and sublimation.
What is the Ablation Zone?
The lower portion is called the ablation zone because here the amount of new ice added each year is less than the amount lost.
What is the Equilibrium Line?
Separating the two zones is a theoretical equilibrium line, along which accumulation exactly balances ablation.
LC 19-6?
??
Glacier Movement.
• Glacier “flow” is orderly sliding of ice molecules
• Ice under extreme pressure deforms instead of slipping
• Meltwater contributes surface for glacier to slide on
• Flow in response to overlying weight
• Plastic flow and Basal slip
Liquid Flow vs. Glacial Movement?
Despite the fact that glaciers are often likened to rivers of ice, there is little similarity between liquid flow and glacial movement.
Surface Ice?
Surface ice can be characterized as a brittle substance that breaks rather than bends and resists any sort of deformation, evidenced by the cracks and crevasses that often appear at the surface of a glacier.
Ice Below the Surface?
Ice under considerable confining pressure, as below the surface of a glacier, deforms rather than breaks. Moreover, partial melting, due to the stresses within and the pressure at the bottom of the glacier, aids movement because the meltwater sinks to the bottom of the glacier and becomes a slippery layer on which the glacier can slide.
Surface Ice Movement vs. Ice Below the Surface Movement?
Surface ice can be characterized as a brittle substance that breaks rather than bends and resists any sort of deformation whereas ice below the surface of a glacier, deforms rather than breaks.

Also, ice below the surface has partial melting, due to the stresses within and the pressure at the bottom of the glacier, which aids movement because the meltwater sinks to the bottom of the glacier and becomes a slippery layer on which the glacier can slide.
What is the Plastic Flow of Ice?
When a mass of ice attains a thickness of about 50 meters—less on steep slopes—the plastic flow of ice begins in response to the overlying weight.

The entire mass does not move uniformly; rather, there is an oozing outward from around the edge of an ice sheet or downvalley from the toe (the end) of an alpine glacier.
What is Basal Slip?
A second kind of glacier movement is basal slip at the bottom of the glacier, in which the entire mass slides over its bed on a lubricating film of water. The glacier more or less molds itself to the shape of the terrain over which it is riding.
Movement of Glaciers?
Glaciers usually move very slowly.

The flow of glaciers are often erratic, with irregular pulsations and surges over a short span of time.

All parts of a glacier do not move at the same rate. The fastest-moving ice is that at and near the surface, with speed generally decreasing with depth. If the glacier is confined, the way a valley glacier is, for instance, the center of the surface ice moves faster than the sides, which is similar to streamflow patterns.
Glacier Flow vs. Glacier Advance?
As long as a glacier exists, the ice in it is flowing, either laterally outward or downhill. This does not necessarily mean that the outer edge of the ice is advancing, however. The ice in a glacier always moves forward, but the outer margin of th...
As long as a glacier exists, the ice in it is flowing, either laterally outward or downhill. This does not necessarily mean that the outer edge of the ice is advancing, however. The ice in a glacier always moves forward, but the outer margin of the glacier may or may not be advancing, depending on the balance between accumulation and ablation. Even in a retreating glacier (one whose outer margin is retracting toward its point of origin due to heavy ablation), the ice is flowing forward.

During wetter or cooler periods when there is a great accumulation of ice, a glacier can flow farther before it finally wastes away, and so the outer margin of the glacier advances.
During warmer or drier periods when the rate of ablation is increased, the glacier continues to flow, but it wastes away sooner, and so the end or terminus of the glacier retreats.
LC 19-7?
??
What are some of the ways Glaciers Affect Topography
The Effects of Glaciers on Topography?
As glaciers move across a landscape, they can reshape the topography through the erosion, transportation, and deposition of rock.
Erosion by Glaciers. (LS)
– Volume and speed determine success of glacial erosion
– Erosive power of moving ice slightly larger than that of water
– Glacial Plucking—picking up of rock material through refreezing of meltwater
– Glacial Abrasion—bedrock worn down by rock debris embedded in glacier
– Subglacial meltwater erosion
The Amount of Erosion by Glaciers?
The amount of erosion caused by a glacier is
roughly proportional to the thickness of the
ice and its rate of flow.
The Depth of Erosion by Glaciers?
The depth of the erosion is limited in part by the structure and texture of the bedrock and in part by the relief of the terrain.
Discuss Glacier Erosion (Erosion by Glaciers).
The direct erosive power of moving ice is greater than that of flowing water but not remarkably so. As the slowly moving ice scrapes against bedrock, friction between rock and ice causes the lowermost ice to melt, and the layer of water created reduces the pressure on the rock. This water can refreeze around rocky protrusions, however, and the refrozen ice can exert a significant force as it is pushed by the ice behind it.
What is Glacial Plucking?
Probably the most significant erosive work of glacial ice is accomplished by this glacial plucking.
Rock fragments beneath the ice are grasped as meltwater refreezes in bedrock joints and fractures where frost wedging further loosens the rock.
As the ice moves along, these particles are plucked out and dragged along.
This action is particularly effective on leeward slopes (slopes facing away from the direction of ice movement) and in well-jointed bedrock.

(picking up of rock material through refreezing of meltwater)
What is Glacial Abrasion?
Glaciers also erode by abrasion, in which the bedrock is worn down by the rock debris being dragged along in the moving ice.
Abrasion mostly produces minor features, such as polished surfaces when the bedrock is of highly resistant material and striations (fine parallel indentations) and grooves (indentations deeper and larger than striations) in less resistant bedrock

(bedrock worn down by rock debris embedded in glacier)
Glacial Plucking vs. Glacial Abrasion?
Whereas plucking tends to roughen the underlying surface, abrasion tends to polish it and to dig striations and grooves.
Subglacial Meltwater Erosion?
A third process also contributes to glacial erosion: Meltwater streams flowing below the glacier not only transport rock, they can erode smooth grooves and channels into the bedrock
Topography Produced/Changed by Glacial Erosions?
In plains areas, the topography produced by glacial erosion may not be clearly visible. Prominences are smoothed and small hollows may be excavated, but the general appearance of the terrain changes little. In hilly areas, however, the effects of glacial erosion are much more notable. Mountains and ridges are sharpened, valleys are deepened and steepened and made more linear, and the entire landscape becomes more angular and rugged.
LC 19-8?
??
Transportation by Glaciers. (LS)
– Glaciers effective to move large rock pieces
– Typically move glacial flour
– Most rock material transported along base of the ice
– Remaining glacial ice free of rock debris
– Role of flowing water on moving ice, melt streams
– Cracks in ice in which streams run—moulins
Transportation by Glaciers
Glaciers are extremely competent, as well as indiscriminate, in their ability to transport rock debris. Glaciers can move immense blocks of rock.

Most of a glacier’s load, however, is not such huge blocks but rather a heterogeneous collection of particles of all sizes, including finely ground rock material known as glacial flour.
What is Glacial Flour?
Finely ground rock material
Transportation by Glaciers?
(Most rock material transported along base of the ice)
Most of the material transported by continental glaciers is plucked or abraded from the underlying surface and so is carried along at the base of the ice. Thus, there is a narrow zone at the bottom of the glacier that is likely to be well armored by rock debris frozen into it, with most of the rest of the glacial ice relatively free of rock fragments.
??
With mountain glaciers, in addition to rock transported within the ice, some of the material is also transported on top of the ice, deposited by rockfall or other forms of mass wasting from the surrounding slopes. With at least some mountain glaciers, mass wasting may supply more rock debris to a glacier than that added by glacial erosion.
Rate of Glacier Transportation (Glacier Transportation Speed)?
A glacier transports its load outward or downvalley at a variable speed. The rate of flow usually increases in summer and slows in winter but also depends on variations in ice accumulation and in the gradient of the underlying slopes.
Discuss Melt Streams.
Another important aspect of transportation by glaciers is the role of flowing water on, in, and under the ice.

During the warmer months, streams of meltwater normally flow along with the moving ice. These streams may run along the surface of the glacier until they find cracks or crevasses into which to plunge (moulins), continuing their flow as a subglacial stream either within the ice or along the interface between glacier and bedrock.
Wherever such streams flow, they transport rock debris, particularly smaller particles and glacial flour, providing an effective mechanism for shifting debris from the ice surface to a position within or at the bottom of the glacier.
Further, where subglacial streams encounter finely ground rock along the bottom of a glacier, the lubricating effect can accelerate the flow of ice.
Even if a glacier is retreating, the debris inside it is still carried forward because of the ice flow taking place all through the glacier.
What are Moulins?
Steep drainage shafts in the ice;
Cracks in ice in which streams run
Transport Function of a Glacier?
The transport function of a glacier persists indefinitely unless and until the ice becomes so thin that subglacial obstacles, such as a hill, prevent further flow.
Deposition by Glaciers
– Glaciers move lithospheric material from one region to another in a vastly different form
– Material moved by glaciers—drift
– Till—rock debris deposited by moving or melting ice
– Large boulders that are different from surrounding local bedrock, glacial erratics
What is the Major Role of Glaciers in Landscape Modification?
Probably the major role of glaciers in landscape modification is to pick up rock from one area and take it to a distant region, where it is left in a fragmented and vastly changed form.
What is Drift (Glacial Drift)?
All material carried and deposited by glaciers.

The general term for all material moved by glaciers is drift.

Refers to any material deposited by glaciers and/or their meltwater.
What is Till?
Rock debris directly deposited by moving or melting ice, with no meltwater redeposition involved
Direct Deposition by Glacial Ice?
Direct deposition by ice is usually the result of melting around the margin of an ice sheet or near the lower end of a mountain glacier, but it is also accomplished whenever debris is dropped on the ground beneath the ice, especially in the ablation area.

In either case, the result is an unsorted and unstratified agglomeration of fragmented rock material.

Most of the fragments are angular because they have been held in position while carried in the ice (and so had little opportunity to become rounded by frequent impact the way pebbles in a stream would) or were deposited on top of the ice by mass wasting.
What are Glacial Erratics?
Outsize boulders included in the glacial till, which may be very different from the local bedrock.

Sometimes outsized boulders are deposited by a retreating glacier. Such enormous fragments, which may be very different from the local bedrock, are called glacial erratics
LC 19-19?
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Secondary Deposition by Meltwater:
• Deposition of Meltwater
– Large portion of debris carried by glaciers deposited or redeposited by meltwater
– Subglacial streams from glaciers carry sedimentary material
– Glaciofluvial deposition
Peculiarities of Glacial Stream Runoff?
Glacial stream runoff has several peculiarities that set meltwater streams apart from other kinds of natural waterways. Such peculiarities include:
peak flows in midsummer,
distinct day-and-night differences in volume,
large silt content,
and occasional floods
Deposition of Meltwater?
Much of the debris carried by glaciers is eventually deposited or redeposited by meltwater.

In some cases, this is accomplished by subglacial streams issuing directly from the ice and carrying sedimentary material washed from positions in, on, or beneath the glacier. (Subglacial streams from glaciers carry sedimentary material)

Much meltwater deposition, however, involves debris that was originally deposited by ice and subsequently picked up and redeposited by the meltwater well beyond the outer margin of the ice.

Such glaciofluvial deposition occurs around the margins of all glaciers, as well as far out in some periglacial zones.
What is Glaciofluvial Deposition?
The action whereby rock debris that is carried along by glaciers is eventually deposited or redeposited by glacial meltwater.

Glaciofluvial deposition occurs around the margins of all glaciers, as well as far out in some periglacial zones.
Continental Ice Sheets?
Ice sheets are the third most extensive feature on the planet (oceans and continents are the first two extensive features)

The actions of Continental Ice Sheets during the Pleistocene significantly reshaped both the terrain and the drainage of nearly 1/5 of the total surface area of the continents
Development and Flow of Ice Sheets (LS)
– Pleistocene ice sheets originated in midlatitudes and subpolar regions
– Ice flowed outward from center of accumulation
– Ice sheets ebbed and flowed with changing climate
Where did the Pleistocene Ice Sheets Originate?
Pleistocene ice sheets, with the exception of the one covering Antarctica, did not originate in the polar regions. Rather, they developed in subpolar and midlatitude locations and then spread outward in all directions, including poleward.
Development and Flow of Ice Sheets
Several (perhaps several dozen) centers of original ice accumulation have been identified.

The accumulated snow/névé/ice eventually produced such a heavy weight that the ice began to flow outward from each center of accumulation.
Flow of Ice Sheets
The initial flow was channeled by the preexisting terrain along valleys and other low-lying areas, but in time the ice developed to such depths that it overrode almost all preglacial topography.

Eventually the various ice sheets coalesced into only one, two, or three massive sheets on each continent.
These vast ice sheets flowed and ebbed as the climate changed, always modifying the landscape with their enormous erosive power and the great masses of debris they deposited.

The elaborate result was nothing less than a total reshaping of the land surface and a total rearrangement of the drainage pattern.
Erosion by Ice Sheets (LS)
– Principal topography from ice sheet is gently undulating surface
– Valley bottoms created from moving ice
– Roche Mountonnée,: Stoss side vs. Lee side
– Postglacial landscape has low relief but is not absolutely flat
Erosion by Ice Sheets: What is the Principal Topographic Result from Ice Sheet Erosion?
Except in mountainous areas of great initial relief, the principal topography resulting from the erosion caused by an ice sheet is a gently undulating surface
Erosion by Ice Sheets
The most conspicuous (visible) features are valley bottoms gouged and deepened by the moving ice.

Such troughs are deepest where the preglacial valleys were oriented parallel to the direction of ice movement, particularly in areas of softer bedrock.
Erosion by Ice Sheets: Lakes?
Even where the preglacial valley was not oriented parallel to the direction of ice flow, however, glacial gouging and scooping normally produced a large number of shallow excavations that became lakes after the ice disappeared.

Indeed, the postglacial landscape in areas of ice-sheet erosion is notable for its profusion of lakes.
What is a Roche Moutonnée?
Hills are generally sheared off and rounded by the moving ice. A characteristic shape produced by both continental ice sheets and mountain glaciers is the roche moutonnée, which is often produced when a bedrock hill is overridden by moving ice.

The stoss side (facing in the direction from which the ice came) of a roche moutonnée is smoothly rounded and streamlined by grinding abrasion as the ice rides up the slope, but the lee side (facing away from the direction from which the ice came) is shaped largely by plucking, which produces a steeper and more irregular slope.
The Stoss Side of a Roche Moutonnée vs. The Lee Side of a Roche Moutonnée.
The stoss side (facing in the direction from which the ice came) of a roche moutonnée is smoothly rounded and streamlined by grinding abrasion as the ice rides up the slope.
But, the lee side (facing away from the direction from which the ice came) is shaped largely by plucking, which produces a steeper and more irregular slope.
The Stoss Side of a Roche Moutonnée vs. The Lee Side of a Roche Moutonnée: The Stoss Side of a Roche Moutonnée?
The side facing in the direction from which the ice came
The Stoss Side of a Roche Moutonnée vs. The Lee Side of a Roche Moutonnée: The Lee Side of a Roche Moutonnée?
The side facing away from the direction from which the ice came
The Formation of a Roche Moutonnée.
The glacier rides over a resistant bedrock surface, smoothing the stoss side by abrasion and steepening the lee side by plucking. When the ice has melted, an asymmetrical hill is the result.
The glacier rides over a resistant bedrock surface, smoothing the stoss side by abrasion and steepening the lee side by plucking. When the ice has melted, an asymmetrical hill is the result.
Postglacial Landscape?
The postglacial landscape produced by ice sheets is one of relatively low relief but is not absolutely flat.

The principal terrain elements are ice-scoured rocky knobs and scooped-out depressions.

Soil and weathered materials are largely absent, with bare rock and lakes dominating the surface.

Stream patterns are erratic and inadequately developed because the preglacial drainage system was deranged by ice erosion.

Once eroded by the passing ice sheet, however, most of this landscape was subjected to further modification by glacial deposition. Thus, the starkness of the erosional landscape is modified by depositional debris.
Deposition by Ice Sheets (LS)
– Irregular, uneven surface of deposition, till plain
– Moraines—land consisting primarily of till
– Three Types of Moraines
• Terminal Moraine—marks outermost limit of glacial advance
• Recessional Moraine—position where ice front is stabilized
• Ground Moraine—large quantities of till laid down from under a glacier instead of from its edge, kettles
– Drumlins
Deposition by Ice Sheets?
In some cases, the till transported by ice sheets is deposited heterogeneously and extensively, without forming any identifiable topographic features; a veneer of unsorted debris is simply laid down over the preexisting terrain. This veneer is sometimes quite shallow and does not mask the original topography. In other cases, till is deposited to a depth of several hundred meters, completely obliterating the shape of the preglacial landscape. In either case, deposition tends to be uneven, producing an irregularly undulating surface of broad, low rises and shallow depressions. Such a surface is referred to as a till plain.
What is a Till Plain?
Irregular, uneven surface of deposition
What are Moraines?
Moraine is a general term for glacier-deposited landforms composed entirely or largely of till.

Moraines typically consist of irregular rolling topography rising some small height above the surround- ing terrain.
Moraines are usually much longer than they are wide, although the width can vary from m to km.
Some moraines are distinct ridges, whereas others are much more irregular in shape.
Their relief is not great, varying from a few meters to a few hundred meters.
When originally formed, moraines tend to have relatively smooth and gentle slopes, which become more uneven with the passage of time, as the blocks of stagnant ice, both large and small, included within the till eventually melt, leading to the collapse of the surface of the moraine.
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In many instances, glacial sediments are laid down in more defined patterns, creating characteristic and identifiable landforms 

Glacier-deposited and glaciofluvially deposited features of a landscape as a continental ice sheet retreats.
In many instances, glacial sediments are laid down in more defined patterns, creating characteristic and identifiable landforms

Glacier-deposited and glaciofluvially deposited features of a landscape as a continental ice sheet retreats.
What are the Three Types of Moraines?
Three types of moraines are particularly associated with deposition from continental ice sheets, although all three may be produced by mountain glaciers as well:
1. Terminal Moraine
2. Recessional Moraine
3. Ground Moraine
Terminal Moraine
(marks outermost limit of glacial advance)

A terminal moraine is a ridge of till that marks the outermost limit of glacial advance.

It can vary in size from a conspicuous ridge tens of meters high to a low, discontinuous wall of debris.

A terminal moraine is formed when a glacier reaches its equilibrium point and so is wasting at the same rate that it is being nourished.

Although the toe of the glacier is not advancing, the interior continues to flow forward, delivering a supply of till.

As the ice melts around the margin, the till is deposited, and the moraine grows
Moraine growth at the terminus of a glacier
Moraine growth at the terminus of a glacier. Rock is carried within the ice, emerging at the end of the glacier where it is deposited in a moraine. Some debris also moves on top of the ice. The final diagram represents the situation after the ice ...
Moraine growth at the terminus of a glacier. Rock is carried within the ice, emerging at the end of the glacier where it is deposited in a moraine. Some debris also moves on top of the ice. The final diagram represents the situation after the ice has melted.
Recessional Moraine
(position where ice front is stabilized)

Behind the terminal moraine, recessional moraines may develop as the glacier recedes. These are ridges that mark positions where the ice front was temporarily stabilized during the final retreat of the glacier.
Terminal Moraine and Recessional Moraine's Shared Characteristics?
erminal and recessional moraines are collectively referred to as end moraines.

Both terminal and recessional moraines normally occur in the form of concave arcs that bulge outward in the direction of ice movement, indicating that the ice sheets advanced not along an even line but rather as a connecting series of great tongues of ice, each with a curved front
Ground Moraine
The ground moraine is formed when large quantities of till are laid down from underneath the glacier rather than from its edge.

A ground moraine usually means gently rolling plains across the landscape. It may be shallow or deep and often consists of low knolls and shallow kettles.
What are Kettles?
An irregular depression in a morainal surface created when blocks of stagnant ice eventually melt.
Kettles?
Depressions known as kettles can form when large blocks of ice left by a retreating glacier become surrounded or even covered by glacial drift.

After the ice block melts, the morainal surface collapses, leaving an irregular depression.

Today, many kettles remain filled with water as lakes—the water in the kettles is not the same water that was left by the melting ice; the ice simply left the depression that forms the basin of the lake.
The Formation of a Kettle?
The formation of kettles. During deglaciation, isolated masses of ice are often mixed in with the glacial debris and outwash and melt slowly because of the insulation provided by the surrounding debris. When the ice does eventually melt, sizable d...
The formation of kettles. During deglaciation, isolated masses of ice are often mixed in with the glacial debris and outwash and melt slowly because of the insulation provided by the surrounding debris. When the ice does eventually melt, sizable depressions known as kettles may pit the surface of the outwash. Today, many kettles contain water as lakes.
What is a Drumlin?
A low, elongated hill, that is another prominent feature deposited by ice sheets
Drumlins:
Drumlins are much smaller than moraines but composed of similarly unsorted till.

The long axis of the drumlin is aligned parallel with the direction of ice movement.

The end of the drumlin facing the direction from which the ice came is blunt and slightly steeper than the opposite end.

Thus, the configuration is the reverse of that of a roche moutonnée.
The Origin of Drumlins?
The origin of drumlins is complex, but most of them are apparently the result of ice readvance into an area of previous glacial deposition. In other words, they are depositional features subsequently shaped by erosion.

Drumlins usually occur in groups, sometimes numbering in the hundreds, with all drumlins in a group oriented parallel to each other
LC 19-11?
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Glaciofluvial Features. (LS)
– Deposition of debris by ice-sheet meltwater produces features, composed of stratified drift
– Composed of gravel, sand, silt since meltwater is incapable of moving larger material
– Outwash Plains
– Valley Trains
– Kames
– Eskers
– Lakes very common
Glaciofluvial Features?
The deposition or redeposition of debris by ice-sheet meltwater produces certain features both where the sheet covered the ground and in the periglacial region.

These features are composed of stratified drift, deposits that resemble alluvium in that they may appear both layered and sorted to a certain extent because they were carried along by the meltwater. (Deposition of debris by ice-sheet meltwater produces features, composed of stratified drift)

Glaciofluvial features are composed largely or entirely of gravel, sand, and silt because meltwater is incapable of moving larger material.
What is an Outwash Plain?
The most extensive glaciofluvial features are outwash plains, which are smooth, flat alluvial aprons deposited beyond recessional or terminal moraines by streams issuing from the ice
What is a Valley Train?
Beyond the outwash plain, there is sometimes a lengthy deposit of glaciofluvial alluvium confined to a valley bottom; such a deposit is termed a valley train.
What is an Esker?
Long, sinuous ridge of stratified glacial drift composed largely of glaciofluvial gravel and formed by the choking of subglacial streams during a time of glacial stagnation.

Less common than outwash plains, but more conspicuous, are long sinuous ridges of stratified drift called eskers.
What are Kames?
Small, steep mounds or conical hills of stratified drift are found sporadically in areas of ice-sheet deposition.

Kames appear to be of diverse origin, but they are clearly associated with meltwater deposition in stagnant ice.

They are mounds of poorly sorted sand and gravel that probably formed within glacial fissures or between the glacier and the land surface
Lakes in areas that were glaciated during the Pleistocene?
Lakes are very common in areas that were glaciated during the Pleistocene.

The old stream systems were obliterated or deranged by the ice sheets, and water remains ponded in the many erosional basins and kettles, and behind morainal dams.
Mountain Glaciers
Most of the world’s high-mountain regions experienced extensive Pleistocene glaciation, and many mountain glaciers exist today, although most mountain glaciers are getting smaller as a consequence of a warming climate

Mountain glaciers do not usually reshape the terrain as completely as continental ice sheets can, partly because some portions of the mountains protrude above the ice and partly because the movement of mountain glaciers is channeled by the mountains.

However, the effect of glacial action, particularly erosion, on mountainous topography is to create slopes that are often steeper and relief that is greater than the preglacial slope and relief
Mountain Glacier Development and Flow
– Usually form in sheltered depressions near heads of stream valleys
Erosion by Mountain Glaciers
– Basic landform in glaciated mountains is the cirque
– Marks the location where an alpine glacier originated
– Shifting equilibrium line generate quarrying action, bergschrund formation
– Quarried fragments from cirque carried away when ice flows out of cirque
What is a Cirque?
The basic landform feature in glaciated mountains is the cirque, a broad amphitheater hollowed out at the upper most head of a glacial valley by glacial erosion and frost wedging.
The development of a cirque at the head of a valley glacier.
The development of a cirque at the head of a valley glacier.
The development of a cirque at the head of a valley glacier.
The development of a cirque at the head of a valley glacier.
What is a Cirque Glacier?
A small glacier confined to its cirque and not moving down-valley.
What is a Tarn?
Cirque ice melts away, depression that holds water is a tarn
What is an Arête?
Several cirques cut back into interfluve result in spine of rock, an arête
Col
A pass or saddle through a ridge produced when two adjacent glacial cirques on opposite sides of a divide are cut back enough to remove part of the arête between them
Horn
a steep-sided, pyramid-shaped moun- tain peak formed by expansive quarrying of the headwalls where three or more cirques intersect
The development of landforms by mountain glaciation. (a) Landscape before glaciation. (b) Landscape during glaciation. (c) Landscape after glaciation.
The development of landforms by mountain glaciation. (a) Landscape before glaciation. (b) Landscape during glaciation. (c) Landscape after glaciation.
The development of landforms by mountain glaciation. (a) Landscape before glaciation. (b) Landscape during glaciation. (c) Landscape after glaciation.
The development of landforms by mountain glaciation. (a) Landscape before glaciation. (b) Landscape during glaciation. (c) Landscape after glaciation.
Erosion in the Valleys
– Some glaciers never leave cirques
– Principle erosive work is to deepen, steepen, and widen valley
– U-shaped glacial troughs
– Glacial steps result from differences in rock resistance
– Small cliffs and small lakes, paternoster lakes
Glacial Trough
A valley reshaped by an alpine glacier, usually U Shaped
glacial steps
As a result, the down-valley profile of a glacial trough is often marked by an irregular series of rock steps or benches, separated by steep (although usually short) cliffs on the down-valley side. Such landforms are known as glacial steps
Deposition by Mountain Glaciers
– Continental ice sheets more responsible for deposition than mountain glaciation
– The principal depositional landforms associated with mountain glaciation are moraines.
– Lateral Moraines

Moraines resulting from mountain glaciation are much smaller and less conspicuous, however, because they are restricted to glacial troughs
Common types of moraines in mountainous areas.
Common types of moraines in mountainous areas.
Common types of moraines in mountainous areas.
Common types of moraines in mountainous areas.
Lateral Moraines
The largest depositional features produced by mountain glaciation are often lateral moraines; these are well-defined ridges of unsorted debris built up along the sides of valley glaciers
Medial Moraines
Where a tributary glacier joins a main valley glacier, their lateral moraines (and debris carried on top of the ice along the sides of the glaciers) become united at the inter section and often continue together down the middle of the combined glacier as a dark band of rocky debris known as a medial moraine
Distribution of Moraines around a Valley Glacier
Distribution of Moraines around a Valley Glacier
Distribution of Moraines around a Valley Glacier
Proglacial Lake
Where ice flows across a land sur- face, the natural drainage is either impeded or blocked, and meltwater from the ice can become impounded against the ice front, forming a proglacial lake.

A lake formed when ice flows across or against the general slope of the land and the natural drainage is impeded or completely blocked so that meltwater from the ice becomes impounded against the ice front.
The Periglacial Environment
• Periglacial—on the perimeter of glaciation
• Permafrost presence
• Frozen ground exists in Alaska, Canada, Russia
• Extends to great depths
• Patterned ground
• Proglacial lakes
Periglacial—
on the perimeter of glaciation
Causes of the Pleistocene Glaciations
• What initiates ice ages?
• Any plausible theory must account for four main characteristics
– Ice accumulation is in both hemispheres but is non-uniform
– Concurrent development of pluvial conditions in dry land areas
– Multiple ice advance and retreat cycles
– Eventual total deglaciation
Any complete theory of the causes of the Pleistocene glaciations must be able to account for four main glacial characteristics:
1. Ice accumulation is in both hemispheres but is non-uniform
2. Concurrent development of pluvial conditions in dry land areas
3. Multiple ice advance and retreat cycles
4. Eventual total deglaciation
Cold vs. Warm climate for glaciation
We know that glaciers grow when there is a net accumulation of snow over a period of time and that glacierswaste away when summer melting exceeds winter snowfall.

Beyond that simplistic statement, however, in some cases it is not always clear whether a colder climate would be more conducive to glaciation than a warmer but wetter one

Although colder conditions would inhibit summer wastage and thus enhance the longevity of the winter accumulation, cold air cannot contain much water vapor.

Hence, warmer winters would favor increased snowfall, whereas cooler summers are needed for decreased melting.
Are we still in an ice age?
Are we still in an ice age?
Glaciers impact the landscape through ice mass motion and associated erosion
Glaciers impact the landscape through ice mass motion and associated erosion
There are two primary well known eras for glaciation, the Pleistocene and contemporary glaciation
There are two primary well known eras for glaciation, the Pleistocene and contemporary glaciation
During the Pleistocene, ice occupied a third of the total land mass of the Earth
During the Pleistocene, ice occupied a third of the total land mass of the Earth
Antarctica and Greenland make up a large percentage of the contemporary glaciation
Antarctica and Greenland make up a large percentage of the contemporary glaciation
There are two primary types of glaciers, continental ice sheets and mountain glaciers
There are two primary types of glaciers, continental ice sheets and mountain glaciers
Glacier formation involves the process of converting snow to ice through intense pressure and snow accumulation
Glacier formation involves the process of converting snow to ice through intense pressure and snow accumulation
Glaciers move via sliding along a land surface; meltwater helps enhance the ability of glaciers to move
Glaciers move via sliding along a land surface; meltwater helps enhance the ability of glaciers to move
Glaciers have two primary erosive effects
Glaciers have two primary erosive effects
Glaciers are capable of transporting large rock material as well as glacial flour
Glaciers are capable of transporting large rock material as well as glacial flour
Glaciers deposit material through their transport as well as meltwater
Glaciers deposit material through their transport as well as meltwater
Continental ice sheets have a unique set of erosive and depositional characteristics
Continental ice sheets have a unique set of erosive and depositional characteristics
Moraines are glacier-deposited landforms that consist entirely or largely of till
Moraines are glacier-deposited landforms that consist entirely or largely of till
Glaciofluvial features play an important role in the distribution of deposited glacier material
Glaciofluvial features play an important role in the distribution of deposited glacier material
Mountain glaciers have limited erosive and depositional characteristics
Mountain glaciers have limited erosive and depositional characteristics
Valley effects of mountain glaciers can drastically alter the landscape in these regions
Valley effects of mountain glaciers can drastically alter the landscape in these regions
The region surrounding a glacier that is modified by the glacier but not under it is called the periglacial
The region surrounding a glacier that is modified by the glacier but not under it is called the periglacial
There are numerous unique characteristics of the periglacial environment
There are numerous unique characteristics of the periglacial environment
The exact causes of ice ages, including the Pleistocene, are unknown, though many theories hypothesize about the different effects that could have contributed
The exact causes of ice ages, including the Pleistocene, are unknown, though many theories hypothesize about the different effects that could have contributed
It is unknown if we are still in an ice age
It is unknown if we are still in an ice age