Glaciers and Climate Change Chapter 13 Geology Today

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Glaciers and Climate Change Chapter 13 Geology Today Barbara W. Murck Brian J. Skinner

Glaciers and Climate Change Chapter 13 Geology Today Barbara W. Murck Brian J. Skinner Mount Fairweather, Glacier Bay, Alaska N. Lindsley-Griffin, 1999

Glaciers are permanent bodies of ice (recrystallized snow) that show evidence of movement due

Glaciers are permanent bodies of ice (recrystallized snow) that show evidence of movement due to gravity. Fig. 14. 11, p. 410 N. Lindsley-Griffin, 1999

Types of Glaciers Ice sheets are continent-sized glaciers that overwhelm nearly all the land

Types of Glaciers Ice sheets are continent-sized glaciers that overwhelm nearly all the land within their margins. Antarctica, one of two present-day ice sheets (the other is Greenland) N. Lindsley-Griffin, 1999

Types of Glaciers Ice caps cover mountain highlands, or low-lying land at high latitudes

Types of Glaciers Ice caps cover mountain highlands, or low-lying land at high latitudes Vatnajokull N. Lindsley-Griffin, 1999 Ice caps in Iceland (Fig. 14. 11, p. 410)

Types of Glaciers Types of glaciers are determined by their size and location Confined

Types of Glaciers Types of glaciers are determined by their size and location Confined to a valley? Spread over mountain tops? Cover a continent? Fig. 14. 11, p. 410 N. Lindsley-Griffin, 1999

Types of Glaciers Valley glaciers flow down valleys. Pressure of ice at higher elevations

Types of Glaciers Valley glaciers flow down valleys. Pressure of ice at higher elevations pushes them down below snowline. Denali National Park, Alaska (Fig. 14. 11, p. 411) N. Lindsley-Griffin, 1999

Types of Glaciers Piedmont glaciers form large lobes where valley glaciers come together and

Types of Glaciers Piedmont glaciers form large lobes where valley glaciers come together and flow onto lowlands. Gorner Glacier, Swiss Alps (Fig. 14. 11, p. 410) N. Lindsley-Griffin, 1999

Types of Glaciers Fjord glaciers occupy fjords: glaciercarved troughs in bedrock that fill with

Types of Glaciers Fjord glaciers occupy fjords: glaciercarved troughs in bedrock that fill with seawater as the glacier retreats Southwestern Greenland (Fig. 14. 11, p. 411) N. Lindsley-Griffin, 1999

Types of Glaciers N. Lindsley-Griffin, 1999 Cirque glaciers are confined to cirques: bowl-shaped depressions

Types of Glaciers N. Lindsley-Griffin, 1999 Cirque glaciers are confined to cirques: bowl-shaped depressions where snow and ice accumulate on mountains. Denali National Park, Alaska (Fig. 14. 11, p. 410)

How Glaciers Form 1) Fresh snow is fluffy and porous. The delicate crystal points

How Glaciers Form 1) Fresh snow is fluffy and porous. The delicate crystal points evaporate; their vapor fills pore spaces. 2) The ice crystals gradually become smaller, rounder, denser. 3) Successive snowfalls bury and compact the ice crystals until they recrystallize into a metamorphic rock - glacier ice Fig. 14. 13, p. 413 N. Lindsley-Griffin, 1999

Alpine or valley glaciers form on high mountains at all latitudes, wherever snow remains

Alpine or valley glaciers form on high mountains at all latitudes, wherever snow remains all year. Snow granular ice glacial ice (fused, massive)

Glacier Budgets Positive budget - glacier grows Negative budget - glacier shrinks Accumulation zone

Glacier Budgets Positive budget - glacier grows Negative budget - glacier shrinks Accumulation zone - snow builds up to form glacier ice at the head Zone of ablation - snow melts and evaporates at the terminus Lutgens & Tarbuck; N. Lindsley-Griffin, 1999 See Fig. 14, p. 414

Glacier Budgets Glacier will advance if more ice is added to head than is

Glacier Budgets Glacier will advance if more ice is added to head than is removed at terminus Glacier will retreat if more ice is removed at terminus than is added at head. N. Lindsley-Griffin, 1999 Fig. 14, p. 414

Glacier Movement Ice crystals move by internal creep. Stress imposed by weight of overlying

Glacier Movement Ice crystals move by internal creep. Stress imposed by weight of overlying ice aligns the crystal axes. Internal cleavage planes slip past each other like a deck of playing cards. N. Lindsley-Griffin, 1999 Fig. 14. 15, p. 415

Glacier Movement Glaciers flow by internal creep at the center, away from the sides.

Glacier Movement Glaciers flow by internal creep at the center, away from the sides. Flow is slower along sides and base, where they are abrading. Shallow ice is brittle, it cracks to form crevasses under tensional stress. Fig. 14, p. 414 N. Lindsley-Griffin, 1999

Glacier Movement Basal sliding, in which the glacier slides along its bed, occurs when

Glacier Movement Basal sliding, in which the glacier slides along its bed, occurs when meltwater lubricates the base of the glacier. Basal sliding may be one cause of glacial surges - very rapid advances. Fig. 14, p. 414 N. Lindsley-Griffin, 1999

Glacial Landscapes The landscapes that result depend on the type of glaciation. Ice sheets

Glacial Landscapes The landscapes that result depend on the type of glaciation. Ice sheets and ice caps override nearly everything in their reach - they smooth out the landscape. Valley or alpine glaciers carve valleys deeper and wider, and leave sharp ridges and peaks between the valleys. N. Lindsley-Griffin, 1999

Glacial Erosion Lutgens & Tarbuck; N. Lindsley-Griffin, 1999 Ice abrades on the upstream side;

Glacial Erosion Lutgens & Tarbuck; N. Lindsley-Griffin, 1999 Ice abrades on the upstream side; plucks on the downstream side. Ice flow on uneven bedrock surface

Glacial Erosion Abrasion smooths rock surfaces to form glacial polish; scrapes surfaces to make

Glacial Erosion Abrasion smooths rock surfaces to form glacial polish; scrapes surfaces to make grooves, striations Striated cobbles, Peyto Glacier, Alberta Glacial polish, Sierra Nevada Range, California N. Lindsley-Griffin, 1999

Erosion by Pleistocene ice sheets: Scooped out Great Lakes and the Finger Lakes of

Erosion by Pleistocene ice sheets: Scooped out Great Lakes and the Finger Lakes of New York U. S. G. S. , N. Lindsley-Griffin, 1999

Erosion by Pleistocene ice sheets: Produced the smooth, scoured topography of the Canadian Shield

Erosion by Pleistocene ice sheets: Produced the smooth, scoured topography of the Canadian Shield U. S. G. S. , N. Lindsley-Griffin, 1999

Glacial Erosion Landscapes shaped by valley glaciers = Alpine glaciers Horn Arete Tarn Cirque

Glacial Erosion Landscapes shaped by valley glaciers = Alpine glaciers Horn Arete Tarn Cirque Hanging Valley V shape U shape Steep, straight valley walls U shape Houghton-Mifflin, 1998; N. Lindsley-Griffin, 1999

Aretes Icefall Cirque Crevasse zone Arete U. S. G. S. , N. Lindsley-Griffin, 1999

Aretes Icefall Cirque Crevasse zone Arete U. S. G. S. , N. Lindsley-Griffin, 1999

Glacial Erosion Alpine glaciation is signaled by: glacial horns and aretes glacial grooves and

Glacial Erosion Alpine glaciation is signaled by: glacial horns and aretes glacial grooves and striations U-shaped valleys Pilot Peak, WY/MT The Matterhorn, Switzerland N. Lindsley-Griffin, 1999

Glacial Erosion N. Lindsley-Griffin, 1999 U-shaped valleys carved by glaciers have broad, flat floors

Glacial Erosion N. Lindsley-Griffin, 1999 U-shaped valleys carved by glaciers have broad, flat floors and steep walls. Beartooth Range, Montana

Glacial Erosion N. Lindsley-Griffin, 1999 Yosemite Valley was carved by a glacier. The famous

Glacial Erosion N. Lindsley-Griffin, 1999 Yosemite Valley was carved by a glacier. The famous waterfalls are streams that flow down hanging valleys and fall to the valley floor. Yosemite National Park, California

Glacial erosion may indicate flow direction Striations -- parallel grooves and scratches gouged into

Glacial erosion may indicate flow direction Striations -- parallel grooves and scratches gouged into bedrock by rock fragments embedded in the glacier N. Lindsley-Griffin, 1999

Roche moutonee Ice Flow N. Lindsley-Griffin, 1999 a glacially carved rock knob that is

Roche moutonee Ice Flow N. Lindsley-Griffin, 1999 a glacially carved rock knob that is smooth on the upstream side, steep and rough on the downstream side.

Glacial Deposits “Stone walls do not good neighbors make. . . ” The stone

Glacial Deposits “Stone walls do not good neighbors make. . . ” The stone walls of New England, immortalized by poet Robert Frost, were built by European settlers clearing glacial boulders from their fields. (The surface layer is till with little or no soil. ) N. Lindsley-Griffin, 1999 Mt. Chocorua, White Mountains, NH

Till - a heterogeneous mixture of Glacial Deposits crushed rock deposited by a glacier.

Till - a heterogeneous mixture of Glacial Deposits crushed rock deposited by a glacier. Poorly sorted: boulders, cobbles, pebbles, sand, silt, rock flour No layering; may be angular or rounded; striated or grooved. Deposited far from source; may rest on striated surface. Pavement outcrop and till, central Maine N. Lindsley-Griffin, 1999

Glacial Deposits Moraines - ridges or piles of debris deposited along glacier edges. Lateral

Glacial Deposits Moraines - ridges or piles of debris deposited along glacier edges. Lateral moraine Medial moraine Moraine Terminal moraine N. Lindsley-Griffin, 1999

Glacial Deposits Terminal moraines form at the ends of glaciers as they retreat. Terminal

Glacial Deposits Terminal moraines form at the ends of glaciers as they retreat. Terminal moraine left behind by retreat of Lobuche Glacier (Fig. 14. 17 D, p. 418) Lateral moraine N. Lindsley-Griffin, 1999

Glacial Deposits N. Lindsley-Griffin, 1999 Lateral moraines are deposited along the sides of valley

Glacial Deposits N. Lindsley-Griffin, 1999 Lateral moraines are deposited along the sides of valley glaciers. Grand Plateau Glacier, St. Elias Mts. , Glacier Bay National Park, Alaska (Fig. 14. 17, p. 418)

Glacial Deposits N. Lindsley-Griffin, 1999 Lateral moraines are deposited along the sides of valley

Glacial Deposits N. Lindsley-Griffin, 1999 Lateral moraines are deposited along the sides of valley glaciers. Grand Plateau Glacier, St. Elias Mts. , Glacier Bay National Park, Alaska (Fig. 14. 17, p. 418)

Glacial Deposits N. Lindsley-Griffin, 1999 Medial moraines form where two valley glaciers merge, joining

Glacial Deposits N. Lindsley-Griffin, 1999 Medial moraines form where two valley glaciers merge, joining their lateral moraines into a stripe of debris in the middle of the glacier. Grand Plateau Glacier, St. Elias Mts. , Glacier Bay National Park, Alaska (Fig. 14. 17, p. 418)

Glacial Deposits N. Lindsley-Griffin, 1999 Medial moraines form where two valley glaciers merge, joining

Glacial Deposits N. Lindsley-Griffin, 1999 Medial moraines form where two valley glaciers merge, joining their lateral moraines into a stripe of debris in the middle of the glacier. Grand Plateau Glacier, St. Elias Mts. , Glacier Bay National Park, Alaska (Fig. 14. 17, p. 418)

Glacial Deposits Besides moraines, retreating glaciers leave behind kames and kettles, drumlins, eskers, outwash

Glacial Deposits Besides moraines, retreating glaciers leave behind kames and kettles, drumlins, eskers, outwash plains Drumlin Outwash Plain Kame Esker Kettle Braided stream N. Lindsley-Griffin, 1999

Glacial Deposits N. Lindsley-Griffin, 1999 Drumlin - streamlined, elongate hill of glacially deposited sediment,

Glacial Deposits N. Lindsley-Griffin, 1999 Drumlin - streamlined, elongate hill of glacially deposited sediment, parallel to ice flow. Blunt end is upstream, tapered end points in direction of ice flow. Drumlin field, Alaska

Glacial Deposits Esker - ridge of sand gravel deposited by a subglacial stream. Kettle-Moraine

Glacial Deposits Esker - ridge of sand gravel deposited by a subglacial stream. Kettle-Moraine State Park, Wisconsin (Fig. 14. 17 B, p. 418) N. Lindsley-Griffin, 1999

Glacial Deposits Glacial erratics, isolated boulders deposited by glaciers, are different than the underlying

Glacial Deposits Glacial erratics, isolated boulders deposited by glaciers, are different than the underlying bedrock. Denali National Park, Alaska (Fig. 14. 17 A, p. 418) N. Lindsley-Griffin, 1999

Kame and kettle topography, Alaska U. S. G. S. ; N. Lindsley. Griffin, 1999

Kame and kettle topography, Alaska U. S. G. S. ; N. Lindsley. Griffin, 1999 Kame - mound of stratified drift deposited by water under or within glacial ice Kettle - depression formed when a buried ice block melted after the glacier retreated

Glacial Deposits Glacial Outwash - stratified sediments deposited by pools or streams of glacial

Glacial Deposits Glacial Outwash - stratified sediments deposited by pools or streams of glacial meltwater. Sorted by size; layered. Look like other alluvial or lacustrine deposits Glacial outwash, Vermont N. Lindsley-Griffin, 1999

Glacial Deposits Varves tend to form in glacial meltwater lakes with seasonal fluctuations in

Glacial Deposits Varves tend to form in glacial meltwater lakes with seasonal fluctuations in sediment supply and wintertime freezing. Each varve consists of: one light sandsilt layer (deposited in summer when streams are active) one dark clay layer (deposited in winter when lake is frozen and quiet) 1 varve = 1 year N. Lindsley-Griffin, 1999

Glacial Deposits Glacial outbursts occur when an active volcano erupts under an ice cap

Glacial Deposits Glacial outbursts occur when an active volcano erupts under an ice cap or sheet. Lava melts ice, meltwater forms large pool under ice cap. Explosive eruption of volcano splits glacier open, releases water in a catastrophic flood. Vatnajokull volcano, Iceland - 1996 (Frontispiece p. 397) N. Lindsley-Griffin, 1999

Periglacial Landforms Ice wedges form in regions of permafrost when surface meltwater seeps into

Periglacial Landforms Ice wedges form in regions of permafrost when surface meltwater seeps into open cracks in the ground and freezes. Wedges grow wider each season as more meltwater flows in during the summer and freezes in winter. N. Lindsley-Griffin, 1999 Fig. 14. 18, p. 420

Periglacial Landforms Individual ice wedges join together to form polygonal patterns. After hundreds of

Periglacial Landforms Individual ice wedges join together to form polygonal patterns. After hundreds of seasons patterned ground results. Patterned ground, Alaska (Fig. 14. 18, p. 420) N. Lindsley-Griffin, 1999

Periglacial Landforms Pluvial lakes are formed by increased rainfall in outlying regions adjoining large

Periglacial Landforms Pluvial lakes are formed by increased rainfall in outlying regions adjoining large ice sheets. In the Western U. S. , during the cooler and wetter climate of the late Pleistocene, Lake Bonneville and Lake Lahontan were the two largest pluvial lakes. N. Lindsley-Griffin, 1999; Lutgens & Tarbuck, J. R. Griffin , 1999

Periglacial Landforms Lake terraces (wave-cut benches) formed by wave action when Lake Lahontan was

Periglacial Landforms Lake terraces (wave-cut benches) formed by wave action when Lake Lahontan was at high water levels during the Pleistocene. Pluvial lake terraces, Nevada N. Lindsley-Griffin, 1999

Causes of Climate Change Three major factors: Tectonic plate motion Long term cyclical variations

Causes of Climate Change Three major factors: Tectonic plate motion Long term cyclical variations in solar radiation (Milankovitch cycles) Changes in Earth’s atmosphere N. Lindsley-Griffin, 1999

Causes of Climate Change Plate motions: Continents at high latitudes favor growth of ice

Causes of Climate Change Plate motions: Continents at high latitudes favor growth of ice sheets : Ice sheets on Gondwana when located over South Pole 276 m. y. a. Ice sheets on Eurasia and North America during Pleistocene Evidence of Gondwanaland ice sheets found on southern continents today Houghton Mifflin 1998; N. Lindsley-Griffin, 1999

Causes of Climate Change Temperatures normally cycle from warm to cold and back again.

Causes of Climate Change Temperatures normally cycle from warm to cold and back again. Glaciation occurs when global temperatures drop a few degrees and remain low long enough for ice sheets to form. N. Lindsley-Griffin, 1999 Fig. 14. 19, p. 421

Global Climate Change Astronomic basis for climatic cycles (Milankovich cycles): 1) variations in Earth’s

Global Climate Change Astronomic basis for climatic cycles (Milankovich cycles): 1) variations in Earth’s orbital distance from the sun, 2) tilt of Earth’s axis varies slightly, 3) Earth’s axis wobbles slowly like a spinning top All 3 act on different time scales that combine in a complicated way to alter amount of solar energy reaching Earth’s surface N. Lindsley-Griffin, 1999 Fig. 14. 21, p. 425

Pleistocene Ice Age Maximum extent of glaciation in the Northern Hemisphere during the ice

Pleistocene Ice Age Maximum extent of glaciation in the Northern Hemisphere during the ice age Lutgens & Tarbuck, J. R. Griffin , 1999

Pleistocene Ice Age North America Coastline during maximum Pleistocene glaciation Location of coast line

Pleistocene Ice Age North America Coastline during maximum Pleistocene glaciation Location of coast line if all the present ice sheets melt Tarbuck & Lutgens, J. R. Griffin , 1999

Pleistocene Ice Age Northern Midwest Blue line = Maximum extent of latest period of

Pleistocene Ice Age Northern Midwest Blue line = Maximum extent of latest period of glaciation (Wisconsin) Red = Maximum extent of earlier Pleistocene glaciation W. Wayne, J. R. Griffin, N. Lindsley-Griffin, 1999

Pleistocene Ice Age Blue line = Maximum extent of latest period of glaciation (Wisconsin)

Pleistocene Ice Age Blue line = Maximum extent of latest period of glaciation (Wisconsin) in Nebraska Red = Maximum extent of earlier Pleistocene glaciation in Nebraska W. Wayne, J. R. Griffin, N. Lindsley-Griffin, 1999

NE Conservation & Survey, J. R. Griffin , 1999 Light green area -Glaciated area

NE Conservation & Survey, J. R. Griffin , 1999 Light green area -Glaciated area

Loess, wind-deposited silt, is common near glaciers because of abundant rock flour In Alaska,

Loess, wind-deposited silt, is common near glaciers because of abundant rock flour In Alaska, loess is forming today Loess, Indian Cave State Park, NE Thick Pleistocene loess, AK

NE Conservation & Survey, J. R. Griffin , 1999 Olive green - Area covered

NE Conservation & Survey, J. R. Griffin , 1999 Olive green - Area covered by Loess