Log entry: environmental studies: earth science 2

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Chapter 14 Glacial and Periglacial Landforms

Visualizing Physical Geography by Timothy Foresman & Alan Strahler

Chapter Overview

Types of Glaciers

Glacial Processes

Glacial Landforms

Periglacial Processes and Landforms

Global Climate and Glaciation

Types of Glaciers

Cryosphere = Portion of the hydrosphere in which water is stored as ice (70% of Earth’s fresh water)

Glacier = Any large natural accumulation of land ice affected by present or past motion

Types of Glaciers

Two broad categories of glaciers are alpine and ice sheets (also called continental glaciers)

Glaciers form in regions with low temperatures and sufficient snowfall (high altitude or latitude)

Types of Glaciers

Alpine glaciers = A glacier formed at high elevation, typically flowing down steep mountain slopes and filling valleys below

Cirque glacier

Valley glacier

Piedmont glacier

Tidewater glacier

Types of Glaciers--Mountains

Ice caps: continuous masses that cover mountaintops

Ice fields: interconnected valley glaciers and protruding ridges or summits

Types of Glaciers

Ice sheet = A large, thick plate of glacial ice that moves outward in all directions

Ice shelf: plates of glacial ice floating on sea

Pieces break off to become icebergs

Glacial Processes

Formation of Glaciers

Firn: granular ice formed by melt and refreeze

Zone of accumulation: where snow accumulates

Zone of ablation: more ice lost than formed

Equilibrium line: rate of snow accumulation = loss from melting and evaporation

Glacial Processes

Formation of Glaciers

Glacier is open system that has dynamic balance between input of accumulated snow and output of melting or evaporation

Input=output, called mass balance, changes each year due to weather

Glacial monitoring

Glacial Processes

Formation of Glaciers

Monitoring the effect of climate change on glaciers

1. Melting glaciers are visually striking evidence of climate change. List, in order, the steps that would lead to a glacier’s retreat due to climate change.

2. How might the loss of the glacier’s ice volume affect downstream ecosystems and human settlements?

McCall Glacier, Alaska, 1958 (left) and 2003 (right)

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Glacial Processes--Movement

Large bodies of ice can move due to gravity

Pressure on ice at bottom changes physical properties of ice, causing it to lose rigidity & become plastic

Basal sliding: layer of liquid water under glacier allows it to move; pressure and friction

Crevasse: brittle surface layer cracks due to movement over ridge or cliff

Insert Figure 14.5.

Glacial Processes

Glacial Erosion and Deposition

Glacial drift = General term for all varieties and forms of rock debris deposited by ice sheets

Stratified drift: layers of sorted & stratified clays, silts, sands and gravel

Till: unstratified mix of rock fragments

Moraine: depostional landform from glacier

Glacier deposits load at lower end where ice melts

Glacial Landforms

Glaciation = Single episode or time period in which ice sheets and alpine glaciers formed, spread, and disappeared

Glacial Landforms

Maximum glaciation during the Ice Age; global sea level about 400 feet lower than it is today. Note Canadian and United States’ ice coverage

Glacial Landforms

Landforms Made by Alpine Glaciers

Before glaciation

Snow accumulates

Glaciation

Melting glaciers

Glacial Landforms

Landforms Made by Alpine Glaciers

Tarn: small lake

Horns: Peaks

Arêtes: Sharp ridges

Col: Notch

Glacial Landforms

Landforms Made by Alpine Glaciers

Glacial trough = deep, steep-sided valley shaped by the action of alpine glaciers.

Hanging valleys: floors of side tributaries lie above valley floor of main glacier

Glacial Landforms

Landforms Made by Alpine Glaciers

Fjord = Narrow, deep ocean inlet that partially fills a glacial trough

Moraine: sediment deposited along front or side of glacier

Lateral moraine: ridge formed by rock waste that falls onto glacier’s edges

Medial moraine: two glaciers meet and lateral moraines combine

Glacial Landforms

Landforms Made by Ice Sheets

During glaciation

Delta

Braided streams

Outwash plain

After melting

Moraines

Eskers: sinuous ridge of sand & gravel

Drumlins: smooth, rounded oval hill

Kames: isolated mound or hill of sand and gravel

Glacial Landforms

Landforms Made by Ice Sheets

Ice sheets are like huge conveyors that move and deposit debris

Formation of a moraine

Terminal moraine: deposit of debris, sand and gravel at front edge of ice sheet

Recessional moraine: deposits formed as ice sheet retreats

Glacial Landforms

Landforms Made by Ice Sheets

Till plain

Lodgement till: compacted by ice sheet

Melt-out till: top layer; looser

Esker: ridge of sand

Drumlin: rounded, oval hill of till

Glacial Landforms

Landforms Made by Ice Sheets

Outwash plain

Kettle: depression formed as sand & gravel built up around stagnant ice

Kame: hill or mound of sediment found on outwash plain

Glacial Landforms

Landforms Made by Glaciation—Human Development

Agriculture

Glaciation can have positive and negative effects

Glacial till in some areas is thin and very stony; makes cultivation difficult

Flat till plains, outwash plains and lake plains can provide very productive agricultural land

Stratified drift

Sources of raw materials (sand and gravel)

Good material for aquifers

Periglacial Processes and Landforms

Periglacial = An environment located in cold climates or near the margins of alpine glaciers or large ice sheets.

Permafrost = Soil, regolith, and bedrock at a temperature that remains below 0°C (32°F) on a perennial basis.

Distribution of permafrost reflects climates of areas

Periglacial Processes and Landforms

Permafrost processes

Active layer: shallow surface layer that thaws with changing seasons

Taliks: pockets of unfrozen ground that occur in zone of discontinuous permafrost or underneath a deep lake or river in zone of continuous permafrost

Ground Ice: frozen water in pore spaces in ground

Gelifluction: Melting of ice in soil during warm periods causes slumping to form terraces and lobes

Ice wedges: form from repeated freeze/thaw cycles

Periglacial Processes and Landforms

Ground Ice and Periglacial Landforms

Pingo: ice dome formed by drained lake

Patterned ground: freeze/thaw

Periglacial Processes and Landforms

Human Interactions with Periglacial Environments

Increased permafrost thaw causes problems for development

Frozen ground contains a lot of CO2 and methane

Thermokarst: water-filled depressions caused by melting

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Global Climate and Glaciation

History of Glaciation

Deglaciation: ice melts at start of milder climate called interglaciation

Interglaciation

Ice Age: period of millions of years of generally cold climates consisting of alternating glaciations & deglaciations

Global Climate and Glaciation

History of Glaciation on Earth

The Ice Age: the Cenozoic Era has seen gradually cooling climate; past 2.5 million yrs has seen the Late Cenozoic Ice Age

Last major glaciation started about 120,000 yrs ago (Wisconsin Glaciation)

More ice coverage increased albedo, which caused more cooling

More water in form of ice, so sea level drops

The Holocene Epoch: period of interglaciation that started at end of Wisconsin period

Rapid warming

Shifting of climate zones and plant coverage

Little Ice Age: from about 1350 to about 1850; not global

Global Climate and Glaciation

History of Glaciation

Triggering periods of glaciation

Continental drift

Changes in Earth/Sun geometry (the Astronomical Hypothesis)

Change in shape of orbit

Tilt angle of Earth’s axis changes

Changes in aphelion & perihelion with seasons

Global Climate and Glaciation

Changes in Earth-Sun geometry

When the tilt of the Earth is greatest (24.5°), what

happens to the intensity of the Earth’s seasons?

a. Summers are cooler and winters are warmer.

b. Summers are warmer and winters are cooler.

c. Summers are warmer and winters are warmer.

d. Summers are cooler and winters are cooler.

Global Climate and Glaciation

Cycles of Glaciation

Cycles in solar revolution and axial rotation mean that annual insolation experienced at a latitude change yearly

Glacial onsets begin with cooler summers that allow snow to accumulate

Albedo increase further cools

Milankovitch Cycle plots the change in insolation by year

Global Climate and Glaciation

Glaciation and Global Warming

Global temperatures increasing

Shrinking polar sea ice

Albedo changes and feedback loops

Changes in Arctic, Antarctica and Larsen’s Ice shelf

Global Climate and Glaciation

Glaciation and Global Warming

If polar sea ice shrinks as predicted by 2050, the zone of continuous permafrost will____.

a. increase in area

b. decrease in area

c. move farther south

d. remain the same