Mcknight Physical Geography Ch 19: Glacial Modification of Terrains

Antarctica influence on the world's environment

-global sea level, oceanic temperature, ocean nutrient content, and patterns of atmospheric circulation all are affected by conditions in Antarctica.

Much of the evidence of past glacial periods

has been eradicated by subsequent geomorphic events, with the result that only the most recent ice age has

Greenland Ice Sheet

ice is much less extensive--(670,000 square miles)--but still

Melt Streams (subglacial streams)

Another important aspect of transportation by glaciers is the role of flowing water on, in, and under the ice. warmer months, streams of meltwater flow along with the moving ice ( find cracks to plunge--including steep drainage shafts in the ice called moulins) within the ice or along the interface between glacier and bedrock. transport rock debris, particularly smaller particles and glacial flour, shifting debris from ice surface to a position within or at the bottom of the glacier. finely ground rock along the bottom of a glacier, the lubricating effect can accelerate the flow of ice.

Warm Currents Melting Ice Shelves (Basal Melt)

2012 West Antarctica ice shelves are losing mass because warm ocean currents are melting the ice from below--a process known as basal melt 2003 and 2008 satellite indicated changes in wind and ocean currents are directing warmer water beneath the ice shelves. Although the loss of ice shelves does not raise global sea level (for the same reason that a floating ice cube does not raise the level of the water in a glass as it melts), changing ice shelves can change in the flow of land-based ice off the continent into the ocean faster then sea level will rise. . Red indicates thicker ice, and blue indicates thinner ice.

What percent of all contemporary erosion and transportation of rock debris (continental denudation) is due to glaciers?

7 percent but small in comparison with fluvial erosion

Contemporary or today's Glaciation coverage

About 10 percent of Earth's land surface (6 million square miles) but more than 96 percent of that total is in Antarctica and Greenland. Something more than two-thirds of all the world's freshwater is at this moment frozen into glacial ice. 1. Greenland Ice Sheet 2. Antarctica Ice Sheet 3. Elsewhere, there are only relatively small ice masses on certain islands in the Canadian Arctic, Iceland, and some of the islands north of Europe. 4. Mountain Glaciers

ICE SHELF

ice reaches the ocean along a massive front, where it sometimes projects out over the sea as an ice shelf

Antarctic Ice Shelves (Ross Ice Shelf largest; Larsen Ice Shelves; Wilkins Ice Shelf, Ronne-Filchner Ice Shelf)

Antarctic ice sheets flow outward from the interior of the continent in all directions toward the sea, icebergs are calved continuously around the perimeter. Some icebergs originate through outlet glaciers, but many are broken off from ice shelves. Great plates of floating ice, particularly in West Antarctica, with the Ross Ice Shelf being the largest 200,000 square miles. Antarctic Peninsula, smaller on Larsen Ice Shelves on the east some 3100 sq miles disintegrated since 1993. 1995 the Larsen-A Ice Shelf collapsed and disappeared 2002, the Larsen-B Ice Shelf collapsed Wilkins Ice Shelf 2008Wilkins Ice Shelf began diseintegrate 2012 a piece of floating ice the size of Rhode Island broke off the Ronne-Filchner Ice Shelf. NASA's Terra satellite. On January 31, 2002, blue "melt ponds" are seen on top of the ice shelf. By March 7, 2002, the ice shelf had disintegrated. The blue area shows the shattered floating ice from the shelf.]

Continental Ice Sheets (nonmountainous Glaciers): ANTARCTICA and GREENLAND (part of Arctic)

Antarctica and Greenland only two exist today Glaciers that form in nonmountainous areas of the continents are called continental ice sheets. Pleistocene epoch had depths of hundreds or even thousands of meters. ice sheets have been the most significant agents of glaciation across the land surface. The ice has great depths in the interior of the sheet but is thinner at the outer edges. OUTLET GLACIERS: Around the margin of the sheet, some long tongues of ice extend between rimming hills to the sea. ICE SHELF: ice reaches the ocean along a massive front, where it sometimes projects out over the sea as an ice shelf ICEBERGS form when the hanging ice of the shelf breaks off and floats away as huge floating ice masses, a process called calving

Disintegration of Antarctic Ice Shelves

Antarctica prominent influence on the world's environment--global sea level, oceanic temperature, ocean nutrient content, and patterns of atmospheric circulation all are affected by conditions in Antarctica. global environment exerts i influence on Antarctica. Over the last half century, average temperatures in the Antarctic have increased by about 2.5°C (4.5°F). Although the complete melting of the Antarctic ice cap is unlikely, the long-term equilibrium between accumulation and wastage of the ice does appear to be changing especially Antarctica's ice shelves.

Apart from the oceans and continents, _________________________ ______________________ sheets are the most extensive features ever to appear on the face of the planet.

Apart from the oceans and continents, continental ice sheets are the most extensive features ever to appear on the face of the planet..

Outlet Glaciers (nonmountainous & part of ice sheets)

Around the margin of the sheet, some long tongues of ice extend between rimming hills to the sea.

Aretes and Cols

Arêtes and Cols: A cirque grows steeper through frost wedging & glacier plucks rock from the head and side walls. Where cirques are close together, the upland interfluve between neighboring cirques is reduced to little more than a steep rock wall. Where several cirques have been cut back into an interfluve from opposite sides of a divide, a narrow, jagged, serrated spine of rock may be all that is left of the ridge crest; this is called an arête (French for "fishbone"; derived from the Latin arista, "spine"). If two adjacent cirques on opposite sides of a divide are being cut back enough to remove part of the arête between them, thesharp-edged pass or saddle through the ridge is referred to as a col ( collum is Latin for "neck";

Truncated spurs

As glacial troughs are formed it grinds protruding spurs.

Glacier Flow versus Glacier Advance

As long as a glacier exists the ice is flowing laterally outward or downhill. This does not necessarily mean that the outer edge of the ice is advancing. 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 wastes away, 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.

Continental Ice sheets reshaped both the _____________ and the ________________ of nearly _______________ of the total surface of the continents.

Continental Ice Sheet reshaped both the terrain and the drainage of nearly one-fifth of the total surface area of the continents.

Dense glacial ice absorbs most wavelengths of _______________ _______________________ but reflects and scateters _____________ _________.

Dense glacial ice absorbs most wavelengths of visible light, but reflects and scatters blue light.

Depositional landforms by Mountain Glaciers

Depositional features are less significant in areas of mountain glaciation than in areas where continental ice sheets have been at work. The high country is often devoid of till; only in the middle and lower courses of glacial valleys can much deposition be found. The principal depositional landforms associated with mountain glaciation are moraines. Terminal and recessional moraines form just as they do with ice sheets but are smaller and restricted to glacial troughs

Kettles

Depressions 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

Glacial Erratics

Direct Deposit (without meltwater) of outsized boulders by a retreating glacier (often different from bedrock).

Every glacier can be divided into two portions on the basis of the balance between ____________________and ____________________

Every glacier can be divided into two portions on the basis of the balance between accumulation and ablation. The upper portion is the accumulation zone because here the amount of new ice from snowfall added each year exceeds the amount lost by melting and sublimation. The lower portion is called the ablation zone because here the amount of new ice added each year is less than the amount lost.

Erosion by Ice Sheets

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. Finger Lakes District of central New York, where a set of parallelstream valleys accentuated by glaciation into a group of long, narrow, deep lakes. The large body of water at upper left is Lake Ontario.

Secondary Deposition by Meltwater (glacioflluvial deposition)

Glacial stream runoff peak flows in midsummer, distinct day-and night differences in volume, large silt content, and occasional floods--that set meltwater streams apart from other kinds of natural waterways. Much of the debris carried by glaciers is eventually deposited or redeposited by meltwater. In some cases, this is a ccomplished by subglacial streams issuing directly from the ice and carrying sedimentary material washed from positions in, on, or beneath the glacier. 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.

Glacial flour

Glaciers can move blocks of rock--the size of houses in some cases--but mainly it moves a heterogeneous collection of particles of all sizes, including finely ground rock material known as glacial flour

Glasial Abrasian

Glaciers erode by abrasion, bedrock is worn down by the rock debris being dragged along in the moving ice, 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 abrasion tends to polish it and to dig striations and grooves (Glacial Polish on granite in Yosemite)

Glacier formation

Glaciers require may begin to develop when there is a net year-to-year accumulation of snow--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 old snow and turns it to ice. After many years ice mass begins to move under the pull of gravity--and a glacier is formed. 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).

Rates of Glacier Movement

Glaciers usually move very slowly; indeed, the adjective "glacial" is synonymous with "exceedingly slow." a few centimeters to several meters per day extreme examples of nearly 100 feet in a 24-hour period have been recorded all parts do not move at the same rate fastest-moving ice is at and near the surface, speed decreasing with depth If confined, center of the surface ice moves faster than the sides, which is similar to streamflow patterns.

Valley glaciers

High country icefields outlets that are tongues of ice that travel down valleys in the mountains. (originate in high icefields)

Roche Moutonee

Hills are often sheared off and rounded by the moving ice. A characteristic shape produced by both continental ice sheets and mountain glaciers is the roche moutonnée, 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. Lembert Dome in Yosemite National Park is an exampe of a roche moutonnee

How many glacial episodes took place during the Plestocene epoch?

In broad terms, the Pleistocene consisted of an alternation of glacial periods (times of ice accumulation) and interglacial periods (times of ice retreat). Current evidence suggests at least 18 or 19 glacial episodes took place during the Pleistocene.

Mountain Glaciers (Valley Glaciers, Piedmont Glaciers, Alpine Glaciers, Cirque Glaciers)

In mountains, ice accumulates in an unconfined sheet submerging underlying topography except perhaps for some protruding pinnacles called nunataks. highland icefields notable in high country of western Canada, southern Alaska, and on various Arctic islands (particularly Iceland). Valley glaciers: Their outlets are often tongues of ice that travel down valleys in the mountains Piedmont glaciers: leading edge of a valley glacier reaches a flat area and escapes from the confines of its valley walls. Alpine glacier: develop individually, high in mountains rather than part of a broad icefield, usually at the heads of valleys. Cirque glaciers: very small alpine glaciers confined to basins where they originate (basin is a cirque). Normally alpine glaciers spill out of originating basins and flow downvalley as long, narrow valley glaciers. Occasionally they extend to the mouth of the valley and become piedmont glaciers.

Moraines deposited from continental ice sheets or mountain glaciers (3 types: terminal, recessional and ground)

MORAINE is a general term for glacier-deposited landforms composed entirely or largely of till. typically irregular rolling topography rising some small height above the surrounding terrain. terminal moraine-ridge of till at outermost limit of glacial advance tens of meters high to a low, discontinuous wall of debris; formed when a glacier reaches its equilibrium point and so is wasting at the same rate that it is being nourished. recessional moraines-behind the terminal moraine develop as the glacier recedes; ridges mark where the ice front was temporarily stabilized Both terminal and recessional moraines form concave arcs that bulge outward in the direction of ice movement ground moraine, formed when large quantities of till are laid down from underneath the glacierrather than from its edge.--gently rolling plains across the landscape. It may be shallow or deep and often consists of low knolls and shallow kettles.

Subglacial Meltwater Erosion

Meltwater streams flowing below can also can erode smooth grooves and channels into the bedrock but the general appearance of the terrain changes little.

Mountain glaciers create __________________ _________________ rather than _____________________the terrain. Continental ice-sheet action tends to __________________and _________________the terrain.

Mountain glaciers create steeper slopes rather than reshape the terrain. Continental ice-sheet action, which tends to smooth and round the terrain.

Blue "melt ponds" seen by NASA

NASA's Terra satellite 2002, blue "melt ponds" are seen on top of the ice shelf. By March 7, 2002, the ice shelf disintegrated.

What was the greatest ice-mass or total area of ice-covered land?

North America -The Laurentide ice covered most of Canada and a large part of northeastern United States; slightly larger than present glacier covering Antarctica. It extended southward into the United States to Long Island, the Ohio River, and the Missouri River. S

Mountain Glaciers today

Other than the two major ice caps, the remainder of the world's present-day glaciers are concentrated in high mountain areas in the Pacific Northwest, and more than half in North Cascade Mountains of Washington In Alaska, there are (29,000 square miles) of glacial ice, about 5 percent of t total area of the state the larges is the Bering Glacier (2000 square miles) and twice size of Rhode Island.

Average temperature increase in the Antarctic

Over the last half century, average temperatures in the Antarctic have increased by about 2.5°C (4.5°F)--much more ' than the average increase in temperature worldwide.

Driftless Area

Part of Wisconsin and 3 adjoining states were 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.

Direct deposition by glacial ice (TILL and Glacial Erratics)

Rock debris deposited directly by moving or melting ice, with no meltwater redeposition (Till fragments)from melt around margin of an ice sheet or near the lower end of a mountain glacier OR when debris is dropped on the ground beneath the ice, especially in the ablation area. If outsized boulders by retreating glacier different from bedrock called glacial erratics. .

What modifications does glaciation make to flat landscapes and mountains?

Slope, drainage, and surficial material are likely to be different from glaciers passing by in flat landscapes. In mountainous areas less so but topography is deepened and steepened, and in many places rounded, by glacial action.

Kames

Small, steep mounds or conical hills of stratified drift are found sporadically in areas of ice-sheet deposition. associated with meltwater deposition in stagnant ice. mounds of poorly sorted sand and gravel formed within glacial fissures or between the glacier and the land surface Morainal surfaces containing a numberof mounds and depressions are called kame-and-kettle topography.

Changing snow to ice

Snow substance that has crystallized from water vapor in the atmosphere and floats to Earth as hexagonal crystals about one-tenth as dense as liquid water. freezing over a period of years, crystalline snow compressed into granular form, and density is doubled then granules may pack & coalesce until it is about half the density of water as névé or firn. Time-pores, air spaces, and neve crystal diminish as air is squeezed out by the weight of the overlying snow; the density approaches 90 percent of that of liquid water, and the material takes on the bluish tinge of glacial ice. This ice continues to change with more air forced out, the density and crystals increasing. Every glacier can be divided into two portions on the basis of the balance between accumulation and ablation. 19-12. 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. The lower portion is called the ablation zone because here the amount of new ice added each year is less than the amount lost. 549 Snow is changed to ice by compression and coalescence, following a sequence from snowflake to granular snow to névé to glacial ice.] Separating the two zones is a theoretical equilibrium line, along which accumulation exactly balances ablation.

Indirect effects of Pleistocene Glaciations

The accumulation of ice, movement and melting of the glaciers effect on topography and drainage. 1. Periglacial processes zone: no glacial ice but erosion and other indirect influences 2. Sea-level changes: raised with ice and lowered with melt 3. Crustal depression: and isostatic adjustments (rebound) 4. Pluvial rain developments: increased moisture with melts

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 the erosion is limited in part by the structure and texture of the bedrock and in part by the relief of the terrain. direct erosive power of 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. 1. Glacial Plucking 2. Glacial Abrasion 3. Subglacial Meltwater Erosion 1. Meltstreams (subglacial streams) 2.Direct Deposition by Glacial Ice 3. Secondary Deposition by Meltwater

Cirques

The basic landform feature in glaciated mountains. A broad amphitheater hollowed out at the uppermosthead of a glacial valley, steep, often perpendicular, head and side walls and a floor that is either flat,gently sloping, or even gouged enough to form a basin. A cirque marks the place where an alpine glacier originated. It is the firstlandform feature produced by alpine glaciation, minor climatic changes may generate much of this quarrying action, along with plucking, mass wasting, and frost wedging. By the middle of summer, a large crevice known as the bergschrund opens at the top of the glacier, exposing part of the headwallto frost wedging. Glacier grows and erosive effectiveness within the cirque increases, and when the glacier begins to extend itself down valley out of the cirque, quarried fragments from the cirque are carried away with the flowing ice Valley glaciers extend down from the highland icefield on top of Mt. Rainier, the highest volcano in the Cascade Range in Washington. When the glacial ice in a cirque has melted away, there is often enough of a depression formed to hold water. Such a cirque lake is called a tarn.

Glaciofluvial Features

The deposition/ redeposition of debris by ice-sheet melt-water produces features of stratified drift, deposits that resemble alluvium appear layered and sorted to a certain because they were carried along by the meltwater. Glaciofluvial features are composed largely or entirely of gravel, sand, and silt because meltwater is rarely capable of moving larger material.

The dominant environmental characteristic of the Pleistocene was the _____________________ of _____________ _____________________________ and __________________________ areas, so that vast amount of ice accumulate in many places.

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. However, the epoch was by no means 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). Current evidence suggests at least 18 or 19 glacial episodes took place during the Pleistocene.

DRIFT

The general term for all material moved by glaciers is drift by deposit or meltwater

The landforms resulting from continental glaciation conform closely to the clearly defined limits of __________________ __________ _______________during the Pleistocene and landforms from mountain glaciation can be found in almost all ______ _______________ areas--even in the tropics.

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.

By the start of the Pleistocene, the ____________________ of climate fluctuations--from ________________ glacial period to ______________interglacial period--had ____________________ and some parts of the ___________________Hemisphere were covered with glaciers.

The most recent findings tell us that by the start of the Pleistocene, the "amplitude" of climate fluctuations--from glacial period to interglacial period--had increased and some parts of the Northern Hemisphere were covered by glaciers.

Pleistocene geologic epoch

The only more recent Ice Age which has influenced contemporary topography and began about 2.5 million years ago and ended about 10,000 years ago

Holocene Epoch

The period since the end of the Pleistocene Epoch approximately 11,000 years ago is identified as the Holocene Epoch. Conceptually, then, the Holocene is either a postglacial epoch or the latest in a series of interglacial interludes.

Till

Unsorted and unstratified agglomeration of angular fragmented rock material from direct deposit of rock without meltwater but from moving glacier, forms around the margin of an ice sheet or near the tower end of a mountain glacier

Plastic Flow of Ice within a Glacier

When a mass of ice thickness about 165 feet ( less on steep slopes) the plastic flow of ice begins in response to the overlying weight. The entire mass does not move uniformly; oozing outward from around the edge of an ice sheet or downvalley from the toe (the end) of an alpine glacier.

Calving

When part of an ice shelf breaks off into an iceberg that floats away

Tarn

a cirque lake

Drumlins

a low, elongated hill, smaller than moraines, composed of similarly unsorted till, end facing the direction from which the ice came is blunt and steeper than the opposite end. Thus, the configuration is the reverse of that of a roche moutonnée. result of ice readvance into an area of previous glacial deposition as depositional features subsequently shaped by erosion, occur in groups, found in central New York and eastern Wisconsin.

Ablation

ablation (wastage of ice through melting and sublimation).

Accumulation

accumulation (addition of ice by incorporation of snow)

Dry Valleys

areas of the Antarctica Ice Sheet (1500 miles) without ice because winds blast away snow and keep precipitation out

Hanging Glacial Troughs (hanging valleys)

as large streams may have tributaries, valley glaciers also may be fed by smaller tributary glaciers but when the ice melts the valleys are different depths & mouths of the tributary valleys perched high along the sides of the major troughs, forming hanging valleys, or more properly, hanging troughs. Typically, streams that drain the tributary valleys must plunge over waterfalls to reach the floor of the main trough. Several of the world-famous falls of Yosemite National Park are of this type

Pleistocene Glaciations extent

at maximum ice covered one-third of the total land area (19 million square miles) up to several thousand meters deep The greatest total area of ice-covered land was in North America. The Laurentide ice covered most of Canada and a large part of northeastern United States Most of western Canada and much of Alaska were covered by an interconnecting network of smaller glaciers. small area in northwestern Canada northern and westernAlaska were never glaciated More than half of Europe was overlain by ice Asia was less extensively covered, ice covered much of Siberia extensive glaciation occurred in most Eurasian mountains Southern Hemisphere, Antarctic ice was slightly more extensive than today a large ice complex covered southernmost South America,the South Island of New Zealand was largely covered with ice. Other high mountain areas all over the world--in central Africa, New Guinea, Hawai'i-- experienced more limited glaciation.

Basal Slip of Ice within a Glacier

at the bottom of the glacier, in which the entire mass slides over its bed on a lubricating film of water. 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.]

Shrinking Glaciers (old fashioned photographs and satellites)

balance between the accumulation of ice and the ablation of ice, glaciers are retreating, and some of the most evidence for this comes not from specialized instruments or satellite measurements, but from old-fashioned photographs. Molina - U.S. Geological Survey (USGS) compared photographs of Alaskan glaciers taken 1890s to the 1970s with new photographs he has taken from the exact same locations; estimates since the most recent peak of glacial ice cover in the 1700s, Alaska has lost about 15 percent of its total glacier cover--a loss of perhaps 1 (3800 square miles) of ice surface area. photographs vegetation patterns changing--extensive plant cover is now obvious. Satellite imagery provides another way to measure changes in glacier size, retreat of glaciers documented: in the Alps, the Himalayas, the Cascades, the Andes, and the Sierra Nevada. Jakobshavn's Isbrae Glacier--Greenland's largest outlet glacier--retreated more than (25 miles) over the last 150 years, and that the Columbia Glacier in southeastern Alaska retreated more than (12 miles) between 1986 and 2011.

Sea-level changes

buildup ice on continents meant less water available to drain into oceans causing a worldwide 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. At the peak of the Pleistocene glaciations, global sea level was about 430 feet lower than today & caused a drainage patterns and topographic development on seashores and - coastal plains , the Bering Strait between present-day Alaska and Russia was a dry land bridge, allowing the migration of both animals and humans

Alpine glaciers

develop individually, high in mountains rather than part of a broad icefield, usually at the heads of valleys.

Glaciers reshape topography through what 3 processes

erosion, transportation, and deposition of rock.

paternoster lakes

excavated depressions on the benches of the glacial steps, forming a sequence called paternoster lakes after a fancied resemblance to beads on a rosary.

Icebergs

form when the hanging ice of the shelf breaks off away as huge floating ice masses float away, a process called calving

Neve or firn

freezing over years crystalline snow compressed into granular form and in time its density may double then granules may pack & coalesce until it is about half the density of water This material is called névé or firn.

Glacial Troughs (U shaped)

glaciers flow down preexisting valleys and reshape. The lower layers of the ice can even flow uphill if blocked permitting rock fragments to be dragged out of depressions in the valley floor and can abrade the sides as well. A conspicuous U-shaped glacial trough in Jotunheimen National Park, Norway. The cross-sectional profile is often changed from a stream-cut "V" shape to an ice-eroded "U" shape flared at the top . valley may be straightened somewhat replacing the sinuous course of the stream with a somewhat straighter, U-shaped glacial trough (some create fjords)

Climate change and contemporary or today's glaciation

global climate change retreat of the Arctic sea ice pack, loss of mass of Greenland's ice sheets due to high temperatures experienced in high latitudes of Northern Hemisphere the last 30 years; variations in both temperature and precipitation. Antarctic ice sheet tells Earth's past climate, climate shift, NASA 2009- Antarctica warming (0.22°F) per decade over the last 50 years (land and satellite measurements)

Pluvial (increased rain) developments

increased moisture on continents due to meltwater runoff, increased precipitation, and decreased evaporation created lakes that left imprints (or are now smaller) such as lakes in the western U.S. as Great Salt Lake in Utah (previously Lake Bonneville and Bonnevile Salt Flats)

Postglacial landscape produced by ice sheets

is one of relatively low relief but not absolute flatness. terrain elements are ice-scoured rocky knobs and scooped-out depressions .Soil and weathered materials are absent bare rock and lakes dominating the surface. Stream patterns are erratic and inadequately developed BUT once eroded by the passing ice sheet, however, most of this landscape was subjected to further modification by glacial deposition.

Piedmont glaciers

leading edge of a valley glacier reaches a flat area and escapes from the confines of its valley walls (originate in high icefields).

Glacier Movement (Plastic Flow and Basal Slip)

little similarity between liquid flow and glacial movement. Surface ice as brittle, breaks rather than bends and resists any sort of deformation (cracks & crevices) However, ice under confining pressure below the surface 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..

Eskers

long sinuous ridges of stratified drift composed largely of glaciofluvial gravel originated when streams flowing throughtunnels in the interior of the ice sheet became clogged, streams deposit much of their load in the tunnel.

Moulins

meltwater or subglacial streams areas of steep drainage shafts in the ice called moulins

What are the two (2) types of glaciers?

mountain glaciers and continental ice sheets.

Glaciers have significant impact on the landscape because

moving ice grinds awayalmost anything in its path: most soil is carried away, and bedrock is polished, scraped, gouged, plucked, and abraded

End of the Pleistocene

now set at 11,70 some Pleistocene glaciers were retreating 9000 years ago the Ice Age may not yet have ended at all best of present knowledge, 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 coincided with the conclusion of what is known in North America as the "Wisconsin" glacial stage (known as the "Würm" in the Alps), approximately 11,000 years ago. The period since then is identified as the Holocene Epoch. Conceptually, then, the Holocene is either a postglacial epoch or the latest in a series of interglacial interludes.

Deposition by Ice Sheets and Till Plains

often 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 and is shallow so does not mask original topgraphy. 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.

Deposits or deposition by glaciers

pick up rock from one area and take it to a distant region, where it is left in a fragmented and vastly changed form. clearly displayed in North America, where an extensive portion of central Canada has been glacially scoured of its soil, regolith, and much of its surface bedrock, leaving a relatively barren, rocky, gently undulating surface dotted with bodies of water. Deposited south in midwestern U.S. making fertile soil and impoverished Canada soil but gave valuable mineral deposits to Canada exposed when glaciers removed soil and regolith.

Nunataks

pinnacles rising above the ice of a highland icefield

Horns (book wrote Homs)

prominent feature of glaciated highland summits is a horn, a steep-sided, pyramid-shaped mountain peak formed by expansive quarrying of the headwalls where three or more cirques intersect The name is derived from Switzerland's Matterhorn, the most famous example of such a glaciated spire. Also Abla Daman.

Glacial steps

resistant rock on the valley floor is gouged less deeply than weaker or more fractured rock so the down-valley profile of a glacial trough is often marked by an irregular series of rock steps or benches, separated by steep cliffs on the down-valley side and can make cliffs for rapids and waterfalls, and paternoster lakes.

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. Plucking roughens surface.

What area was never glaciated during the Pleistocene?

small area northwestern Canada and northern and western Alaska.

Outwash plains (glaciofluvial feature)

smooth, flat alluvial aprons deposited beyond recessional or terminal moraines by streams issuing from the ice, form a braided pattern of channels across the area beyond the glacial front, choked with debris, rapidly lose speed and deposit their load., often become ponds or small lakes. Beyond the outwash plain, there is sometimes a lengthydeposit of glaciofluvial alluvium confined to a valley bottom; such a deposit is termed a valley train.

Antarctica Ice Sheet

the most extensive ice sheet and about 98 percent of its surface is covered with glacial ice, representing almost 90 percent of the world's land-ice total andmore than (13,000 feet) thick in some places and more than 1500 meters (5000 feet) thick over most of the continent. the continent and its ice sheets can be thought of as f two unequal sections separated by the wide upland belt of the Transantarctic Mountains, which extend for some 2500 miles; West Antarctica, the smaller of the two sections, is generally mountainous. a few interior valleys that are ice free ("DRY VALLEYS"). Ty.] 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.

How are glaciers examples of open systems

they have inputs and outputs of both material and energy

Lakes

very common in areas that were glaciated during the Pleistocene. The old stream systems were changed by ice sheets, water remains ponded in erosional basins and kettles, and behind morainal dams. One has only to compare the northern and southern parts of the United States to recognize this fact Most of Europe and the northern part of Asia demonstrate a similar correlation between past glaciation and present-day lakes.

Cirque glaciers

very small alpine glaciers confined to basins where they originate (basin is a cirque).

Periglacial processes or periglacial zone (was in 20 percent of Earth's land area)

was never touched by glacial ice but where indirect i in erosion and deposition by meltwater in were frost weathering caused by the low temperatures and in associated solifluction of frozen subsoil

Isostacy or isostatic adjustment

weight caused crust depression then ice melts for rebound (isostatic adjustment) some portions of Canada and northern Europe are still rising as much as 8 inches per decade.

Crustal depression

weight of ice on continents caused portions of crust to sink as much as (4000 feet) & when ice melted, the crust slowly began to rebound (isostatic adjustment)

Lateral Moraines (the larges depositional features produced by mountain glaciers) and Medial Moraines

well defined ridges of unsorted debris built up along the sides of valley glaciers, is partly material deposited by the glacier and partly rock that falls or is washed down the valley walls; Where a tributary glacier joins a main valley glacier, their LATERAL moraines (and debris carried on top of the ice along the sides ofthe glaciers) become united at the intersection and often continue together down the middle of the combined glacier as a dark band of rocky debris known as a MEDIAl moraine (Medial moraines are sometimes found in groups of three or four running together, indicating that several glaciers have joined to produce a candy-cane effect of black (moraine) and white (ice) bands extending down the valley.

Pleistocene ice sheets development and flow (where did they originate)

with the exception of the one covering Antarctica, did not originate in the polar regions but in they developed in subpolar and midlatitude locations and then spread outward in all directions, including poleward. several centers of original ice accumulation have been identified The accumulated snow/névé/ice weight so the ice began to flow outward from each center of accumulation. initial flow with preexisting terrain like valleys then submerged even the highest points various ice sheets coalesced into only one, two, or three massive sheets on each continent. total reshaping of the land surface and a total rearrangement of the drainage pattern.