7.1 Glaciers

Types of Glaciers Glacier – thick ice mass that forms over hundreds or thousands of years. 15, 000 years ago > 30 % coverage - Today 10 % coverage Valley Glaciers Ice Sheets

Types of Glaciers Valley Glaciers Ice Sheets Ice masses that slowly advance down valleys that were originally occupied by streams A stream of ice that flows btw steep rock walls from a place near the top of the mountain valley Enormous ice masses that flow in all directions from one or more centers and cover everything but the highest land Covering Greenland & Antarctica Continental Ice Sheets B/C they cover large regions where the climate is extremely cold.

How do Glaciers Move? Movement of glaciers = flow Glacier flow happens 2 ways Plastic Flow Movement within the ice Under high pressure > begins to distort & change shape (Plasticity) Basal Slip Gravity causes the entire ice mass to actually slip and slide downhill Crevasses = gaping cracks up to 50 m deep

How glaciers move? Budget of a Glacier The balance of lack of balance btw accumulation at the upper end of the glacier and loss, or wastage, at the lower end Form where more snow falls in winter than can melt during summer Gain & loose ice Snow accumulates > ice forms in the head of the glacier in the zone of accumulation Area of the glacier beyond the snowline = zone of wastage Rates of Glacial Movement Different glaciers = different speeds

Glacial Erosion Plucking Melted water from a glacier refreezes around lumps of broken up rock. The ice then moves downhill and the rock is plucked from the back wall. Abrasion Glacial ice & its load of rock fragments slide over bedrock, they work like sandpaper to smooth out the surface they are moving over.

Rate of glacial erosion is determined by Rate of Glacial Movement Thickness of Ice Shape, abundance, & hardness of the rock fragments in the ice at the base Type of surface under the glacier

Landforms Created by Glacial Erosion

7.2 Deserts

Geologic Processes in Arid Climates Weathering Most of the weathered debris in the deserts have resulted from mechanical weathering Chemical weathering is not totally absent in deserts. Over time clays and thin soils do form The Role of Water In the desert, most streams are ephemeral (the only carry water after it rains) Dangerous flash flooding Lack of vegetation allows water to run off the land even faster

Basin and Range: A desert landscape Playa lake was a basin floor originally before abundant rainfall or snowmelt Playa lakes only last a few days or weeks before they are evaporated and infiltrated Most of the streams in the desert dry up before they reach the ocean Most of the desert erosion occurs due to running water Wind erosion is more significant in deserts than elsewhere, BUT water does most of the erosion in the desert