GEOG 101! 04 Chapter 12 Study Guide
What is till?
Unsorted material deposited directly from glacial ice
What is a zone of fracture?
Uppermost 50 meters; ice is too brittle to flow; causes crevasses
Not all glaciers move at the same _____.
Velocity; some move several meters per day; some take hundreds of years
What are medial moraines?
Visible debris in active ice but not preserved when melted
What is the driftless area of the Upper Midwest?
Glaciers missed on last pass; Steep cliffs, deep river valleys, not flat, no till, not many lakes
What cycles are glaciers part of?
Hydrologic cycle and rock cycle
What are the three general extents/sizes of continental/sheet glaciers?
Ice field, ice cap, and ice sheet
What is permafrost?
If ground is frozen for at least two years; temperature only: not necessarily an abundance of actual ice; groundwater blocked in places
What are the 4 major glacial stages recognized on land?
Nebraskan, Kansan, Illinoian, and Wisconsinian
What does periglacial mean?
No glaciers, but ice action changes the landscape; all year or seasonal; tundra
How long ago was our most recent glacial maximum?
Occurred about 18,000 years ago and ended about 10,000 years ago
What percentage of Earth is covered in glaciers?
10%
What is ground moraine?
A blanket of till
What is the Laurentide Ice Sheet?
A massive sheet of ice that covered millions of square kilometers, including most of Canada and a large portion of the Northern United States (30% of Earth's land)
Melting glaciers result in what percentage of Earth's water?
About 2%
The Antarctic sheet has what percentage of the world's ice?
About 80%
What is glacial drift?
All sediments regardless of how, where, and in what shape deposited
From what do end moraines form?
Alpine glaciers and ice sheets
How do glaciers grow?
Anything left over from the summer before the last winter slowly turns into glacial ice and the glacier expands
What is the zone of accumulation?
Area where a glacier forms; precipitation and avalanches contribute to snowfield; outer limits are defined by the equilibrium line, approximated by the snowline
What is recrystallization?
Rain and summer snowmelt add water and air to the glacier
What is compaction?
Sedimentary-like layers make snow thicker and heavier, increasing pressure of underlying ice
What are drumlins?
Smooth, elongated hills of glacial deposits
What is washed or stratified drift?
Sorted sediments laid down by glacial meltwater
What is a terminal moraine?
The ridge of till at the farthest point reached by a glacier
What is plastic flow (creep)?
With enough pressure, the ice behaves plastically
What are kames?
mounds or steep -sided hills made of sand and gravel
What are kame terraces?
kame formation in a valley
What does glacial abbrasion leave behind?
Rock flour (pulverized rock), glacial striations (grooves in the bedrock), polished surfaces, and chatter marks
What are eskers?
Sand and gravel dropped from meltwater streams
What are outwash plains and valley trains?
Deposited by braided meltwater streams; broad flat plain composed of stratified sand and gravel; often pockmarked with basins or depressions called kettles
What are ice contact deposits?
Deposited by meltwater flowing over, under, within, or against the edge of unmoving ice; coarser and less well-sorted than proglacial deposits
What is an ice field?
Does not cover all topography
What is an ice cap
Domes; do cover all topography
What are clusters of drumlins called?
Drumlin fields
What is the Milankovitch hypoothesis (what drives climate cycles)?
Eccentricity, the shape of the Earth's orbit varies, Obliquity, the angle of the Earth's axis changes, Precession, Earth's axis wobbles
What are outlet glaciers?
Fed by ice caps and ice sheets, but become constrained by mountain valleys; flow over land and often out to the sea
What are tidewater glaciers?
Fed by valley glacier, to ocean
What are Piedmont glaciers?
Fed by valley glaciers; spreads into a lobed sheet on a plain; in broad lowlands at a mountain's base
What are some indirect effects of Ice Age glaciers?
Forced migration of animals and plants, pluvial lakes and rivers, rebounding upward of the crust in former centers of ice accumulation, change in sea level, and 18O concentration in ice/oceanic water
What are Alpine/Valley (non-continuous) glaciers?
High altitude, mountainous areas (Andes, Himalayas, European Alps); streams of ice which flow down a valley from a zone of accumulation at their heads
What are hanging glaciers?
High valley to low valley
What will happen to the sea level if the glaciers melted?
It would rise 60-70 meters
What are erratics?
Large boulders deposited randomly by glaciers
What are Continental/Sheet glaciers (continuous)?
Larger scale than valley glaciers; Greenland and Antarctica; ice flows out in all directions from one or more snow-accumulation centers
The elevation of the snowline varies greatly depending on...
Latitude and aspect
How many major stages are recognized in the ocean?
Less than 10
What is plucking?
Lifting and moving of blocks of rock
Where can you find drumlins?
Many in Michigan, Upper Midwest, and Northeast U.S.
What is an ice sheet?
Massive scale
If too much of the glacier is lost, the glacier ablates by...
Melting, calving, sublimation, wind erosion, and evaporation
Where are glaciers found?
On land or floating on an ice shelf adjacent to land
At the maximum extent of the Pleistocene glaciation period how much of Earth was covered in glaciers?
One-third of Earth's land
What are moraines?
Piles of rocks and debris left when glaciers melt
What causes glaciation?
Plate tectonics; continents were arranged differently in the past; need land in higher altitudes for ice masses to form; changes in oceanic circulation
During which epoch did most major glacial stages occur?
Pleistocene
In what age were glaciers formed?
Pleistocene Ice Age, two to three million years ago
In what two ways do glaciers erode?
Plucking and abrasion
What is abrasion?
Polishing and carving
What is a recessional moraine?
Ridge marking a place where glacial retreat was temporarily halted
What is the glacial budget?
The difference between total accumulation and total ablation for one year
What is a glacier?
Thick, year-round, gravity-mobile ice that originates on land from the repeated accumulation, compaction, and recrystallization of snow
What is a basal slip?
Where meltwater at the base of the glacier lubricates the glacier allowing it to slide - happens in warmer temperatures.
What are fjords?
glacial valleys flooded with seawater and freshwater
