Why should I care about glaciers? Look closely at this graph to understand why we should care? and Glaciation Chapter 11 Temp I. Types of A. Glacier a thick mass of ice that originates on land from the accumulation, compaction, and recrystallization of snow. (ice berg is NOT a glacier but rather just sea ice). I. Types of B. Types of glaciers 1) Valley (or alpine) glacier Flows down a mountain valley from the area of accumulation located high up in the mountains. 2) Ice sheet (or continental ice sheets) Extensively broad glaciers NOT confined to a valley. Two major ice sheets on Earth are over Greenland and Antarctica Ancient ice sheets used to cover parts of North America and Eurasia during last ice age. I. Types of 3) Other types of glaciers Ice caps small ice sheets, not confined to valley Outlet glaciers an arm of an ice cap that is a valley glacier Piedmont glaciers glacier that spreads out after emerging from the valley. 1
I. Types of C. Role of and Sea Level 1) What if glacial ice on Earth melted? Warmer climate = glacial ice melting = sea-level rises. Colder climate = glacial ice sheets growing = sealevel fall. Ex. Antarctic ice sheet 80 % of the world s ice 2/3rds of Earth s fresh water Covers almost 1 ½ times the area of the U.S. If all of it melted, sea level would rise 60 to 70 meters ( 180 feet) A. Glacier Formation - form in areas where more snow falls in winter than melts during the summer B. Formation of glacial ice Snow accumulates every winter, gets buried deeper every year, and compacts Once the snow is buried to around 150 ft (50 m) the snow recrystallizes into ice. Ice flows downhill by gravity C. Glacier Movement (flow) 1) Pulled by gravity basal sliding and internal flow 2) Brittle Flow Found in the uppermost 150 feet (50 meters) Unequal movement causes crevasses (openings in the ice) to form 3) Flows Plastically ice flows plastically. Under pressure, ice behaves as a plastic material (deeper than 150 ft) Ice flows faster at top, and in middle of glacier like a stream. Less friction with ground. D. Rates of glacial movement Slow end = few feet per year High end = few feet per day (Ruth Glacier = 3 ft per day) 2
E. Budget of a glacier 1. Zone of accumulation the area where a glacier forms. (Snow fall exceeds amount snow melted). Snow/ice flows down valley into the next zone: 2. Zone of wastage (ablation) the area where there is a net loss to the glacier due to: a. Melting, (more snow/ice melting than accumulating) or b. Calving the breaking off of large pieces of ice where the glacier has reached the sea (making icebergs) 3. Both zones separated by Snowline. Figure 11.9 4. Balance between accumulation at the upper end of the glacier, and loss at the lower end is referred to as the glacial budget If accumulation exceeds loss (called ablation [ie melting]), the glacial front advances If ablation increases and/or accumulation decreases, the ice front will retreat A. are capable of great erosion and sediment transport 1. Erosion by: a. Plucking lifting of rocks (ex. Tuolumne Meadows) b. Abrasion Rocks in the ice acting like sandpaper to smooth and polish the surface below. Making Glacial striations (grooves in the bedrock) (ex. Tuolumne Meadows) Ancient Glacier Plucking in Tuolumne Meadows, Yosemite National Park Figure 11.17 2. Glacial erosional landforms: U-shaped Glacial valley (glacial trough) Truncated spurs (ridges cut off) Hanging valleys smaller valleys cut off Pater noster lakes Cirques Tarns Fiords Arêtes Horns 3
Figure 11.13 A. Till sediments deposited directly by the ice B. Landforms made of till Moraines Layers or ridges of till Types of Moraines: Lateral moraine on sides of valleys Medial moraine two valley glaciers meet and their lateral moraine merge, called medial moraines. End moraine ( or terminal) at toe of glacier, till pushed up and dropped from conveyor belt of glacier ice movement. Ground moraine underneath glacier. Figure 11.20 IV. of the past A. Ancient Ice Ages Ice covered 30 percent of Earth s land area Many past ice ages cold period with expansive continental glaciers and warm periods like today. One cold-warm cycle about every 120,000 years (for last 2 million years). 4
IV. of the past Tempe B. Effects of Ice Age glaciers Forced migration of animals and plants Changed stream courses Worldwide change in sea level Climatic changes IV. of the past C. Causes: 1. Variations in Earth s orbit, called Milankovitch hypothesis changes in earth orbit cause changes in amount of energy received and therefore cooling and warming. Shape (eccentricity) of Earth s orbit varies Angle of Earth s axis (obliquity) changes Earth s axis wobbles (precession) Changes in climate over the past several hundred thousand years are closely associated with variations in the geometry of Earth s orbit Orbital variations 2. Plate tectonics Different location of continents and oceanic circulation Figure 11.30 5