GLACIERS AND GLACIATION Chapter 14

A. Introduction rely on notes for most of section A

1. Extent of Glaciers

a. Of the 3% of water not in the oceans, about 2.1% is stored as glaciers

b. At present about 10% of all land surface on earth is covered by glaciers

c. At the height of the past Ice Ages, up to 1/3 of all land surfaces were glaciated.

d. For extent of ice sheet in North America.

e. Ice sheet cut diagonally across Ohio such that the NW half of Ohio was covered by the ice sheet.

2. Ice Ages

a. Major episodes of glaciation (Ice Ages) have occurred from time to time throughout geologic history

b. Most recent was the Pleistocene glaciation for which the most evidence remains.

c. During the Pleistocene there were 4-5 major Ice Ages (based on the terrestrial geologic evidence)

d. The last Ice Age began about 100,000 years ago and ended around 10,000-12,000 years ago

3. Changes in Sea Level

a. At the height of the Pleistocene Ice Ages, sea level was about 400 feet lower than today

b. If all of the current glaciers were to melt, sea level would rise by about 200 feet flooding much of the east and gulf coast of the US

B. Movement of Glaciers see p. 325 & 327—Fig 14.5 (for Major Advances)

1. Major Advances/Retreats (Ice Ages/Interglacial Ages) occurs when more snow accumulates in the cold season than is able to melt in the warm season. Favored by:

a. Colder Temperatures (a drop in world wide temperature of only several degrees, if sustained, could cause another Ice Age)

b. Increased precipitation

c. From Fig 14.5, p 327 Know:

i. Equilibrium Line (=Firn line = snow line)—and how it moves during an advance or retreat

ii. Zone of Accumulation

iii. Zone of Ablation

2. Physical Movement of a Glacier pp. 323-324; also p 327-328

a. Note differential movement within ice with depth---may form crevasses

b. Note change of snowflake to firn to solid ice with depth See Fig 14.2, p. 323

c. Note that at depth ice exhibits ductile = plastic behavior and is able to “flow” See Fig 14.3, p 324

d. Ice physically moves by “flowing” downslope due to gravity

C. Types of Glaciers pp. 324-325

1. Continental Glaciers = Ice Sheets

a. Form on land in higher latitudes (near N or S poles)

b. May be extremely large covering continents with ice up to several miles thick.

c. Only 2 major ice sheets today: the Antarctic and the Greenland Ice Sheet

d. The Antarctic Ice Sheet contains about 10 times as much ice as Greenland

e. The weight of an ice sheet causes the ground to subside (sink)---much of the interior of the Greenland land surface is actually below sea level. When the glacier melts the land surface slowly rises again----“isostatic rebound” --- The Great Lakes region is still rebounding

2. Alpine Glaciers (which includes Valley Glaciers, the only type of Alpine glaciers discussed in the book)

a. Form at higher elevations where climate is colder---high mountains—present on every continent

b. Much smaller than ice sheets

c. Consist of Mountain Glaciers, Valley Glaciers and Piedmont Glaciers----only concerned with Valley Glaciers

D. Erosion By Glaciers See328-334

1. Erosional Processes

a. Scraping or Excavating: A Glacier scrapes up everything (soil, regolith) down to bedrock

b. Plucking (= quarrying): prying up loose bedrock

c. Abrasion—rock frozen in the glacier rubs against bedrock

i. Glacial grooves/striations—formed by abrasion

ii. NOTE: Glacial Grooves (like those on Kelley’s Island) tell the direction of movement of the glacier

2. Erosional Features of Alpine Glaciers pay particular attention to figures and captions

Note: Areas that have experienced Alpine Glaciation tend to have sharp, angular features rather that rounded, gentle features. Mountain peaks are shaped more like pyramids than cones.

d. Deep U-shaped valleys

e. Hanging Valleys

f. Fiords

g. Cirques

h. Horns

i. Arêtes

E. Transportation by Glaciers

1. A glacier transports material as “suspended” load by incorporating the material as part of the glacier itself

2. A glacier can transport anything it can pick; size is not a factor---i.e. No limit on competency & no sorting

3. A glacier may physically transport material slowly over long distances---100’s of miles

F. Deposition by Glaciers See pp. 334-340 pay particular attention to figures and captions

1. Till: material dumped directly by ice; poorly sorted, unstratified (not layered)

a. Moraine—book talks about many types, just know the 2 below

i. Ground moraine

ii. End moraine

b. Drumlins—small streamlined hills that can tell the direction that the ice moved

2. Stratified and sorted deposits---those reworked and redeposited by glacial melt waters

a. Outwash plain deposits

b. Eskers

c. Lake Deposits: Lakes form where the drainage of a land surface has not yet achieved equilibrium. Because glaciers scrape everything down to bedrock and then just dump sediment when they melt, glaciation completed destroys an area’s drainage system. After the glaciers retreat it may take thousands of years for equilibrium drainage patterns to be established again and in the interim, there will be lots of lakes.

G. Causes for Global Climate Changes Leading to Ice Ages (or Interglacial Ages) page 340-341 NOTE: Much of my discussion is NOT covered in the textbook

1. Temperature History of the Earth for the last 500,000 years

2. Factors that could lead to another Ice Age

There are many plausible explanations for events that can trigger an ice age and each have their own supporters.

a. Changes in earth’s heat exchange systems (earth’s major wind patterns and ocean currents)

Example: some people now think that the accelerated melting of glaciers at the higher

latitudes may dump enough low density fresh water into the oceans to located “stall” the “conveyer belt” current that distribute heat from the equatorial regions to the polar regions, thus ironically causing an ice age as a result of “global warming”.

b. Pollutants (both natural and those produced by human activity) may have an effect. Whereas increased carbon dioxide, a greenhouse gas, favors global warming, particulate contaminants (volcanic dust, smoke, etc.) prevent some sunlight from reaching the ground and thus cause cooling

c. Position of landmasses relative to the poles (where it is coldest) Glaciers cannot initially form on the oceans, so when the plates are such that there are large landmasses in the polar regions (such as Antarctica today), that favors glaciation. Because plate movement is very slow, the landmasses today have not moved very much since the Pleistocene glaciation, so this is not relevant to these Ice Ages.

d. Milankovitch Theory---at present this is probably the most popular theory to explain Pleistocene glaciation:

Regular periodicities in the earth orbital characteristics causes the amounts of solar energy reaching the earth to vary slightly in a systematic fashion ----

see page 341

3. Impact of Human Activity