glaciers deserts wind v2
V) GLACIERS, DESERTS, and WIND
A) Glaciers: A Part of Two Basic Cycles (Hydrologic and Rock Cycles)
Definition of Terms:
Glacier: A thick ice mass that forms on land over hundreds to thousands of years by accumulation, compaction, recrystallization of snow.
(i) Alpine Glacier: Rivers of ice in mountains which flow from a snow accumulation center.
(ii) Continental Ice Sheets: Ice sheets which flow out in all directions from one or more accumulation centers.
(iii) Piedmont Glaciers: Glaciers which occupy broad lowlands, at the base of mountains, formed when one or more alpine glaciers emerge from mountains onto flat plains.
The Work of Glaciers: Glaciers Erode (pick up), Transport, and Deposit rock debris and sediments.
Glaciers Transport Rocks and Sediment: How Glaciers Move:
(a) Glaciers form where more snow falls in the winter than can melt in the summer. Snow collects in the "Zone of Accumulation" and compresses to form ice.
(b) Zone of Wastage: The lower part of the glacier which experiences net loss of snow and ice.
(c) The ice mass is moved downhill by gravity from the Zone of Accumulation towards the Zone of Wastage.
(d) Snowline: The dividing point (line) between the zones of accumulation and the zone of Wastage—the elevation where the snow from the previous winter completely melts, plus some of the underlying snow.
(e) The top ice moves by blocky displacement, while below 50 meters (165 feet deep) the ice flows via plastic flow.
Work of Glaciers: Glacial Erosion
(a) How Glaciers Erode: Plucking and Abrasion
(i) Plucking: Along the floor of the glacier and at the head of the glacier, water soaks into bedrock cracks, freezes, and releases blocks of rock into glacial ice.
(ii) Abrasion: Rock fragments slide over bedrock like sandpaper.
(b) Rate of Glacial Erosion Controlled by (sandpaper on wood example):
(i) Rate of Glacial Movement (like fast movement of sandpaper).
(ii) Thickness of Glacial Ice (like pressing on sandpaper).
(iii) Shape, abundance, hardness of rock fragments in the base of the glacier (like grit of sandpaper).
(iv) Hardness of underlying country rocks (like sanding soft vs. hard wood).
(v) Time (like duration of sanding wood).
B) Deserts
Desert Weathering: Physical weathering processes prevail over chemical weathering—little water and little vegetation result in minor carbonic acid and little humic acid.
The Role of Water:
(a) Water Erosion: Water is the most important erosional agent.
(i) Rain tends to occur in heavy (high intensity) episodes.
(ii) Water tends to run off quickly in "ephemeral streams."
(iii) Streams are ephemeral (short-lived) because of strong infiltration (deep groundwater) and high evaporation (dry air).
(b) Water Deposition: Desert Landforms
(i) Alluvial Fan: A cone of river-deposited sediment at the mouth of a canyon (Early Stage Desert Erosion).
(ii) Bajada: An apron of Coalescing (interconnected) alluvial fans along a mountain front (Middle Stage Desert Erosion).
(iii) Inselberg: Bedrock knobs surrounded by sediments (typical of Late Stage Desert Erosion).
(iv) Playa: Flat, dry, lake bed.
Role of Wind
(a) Wind Erosion:
(i) Deflation: Lowering of the ground surface by wind lifting and removal of fine, loose sand and silt.
(ii) Saltation: Larger sand grains rolling or skipping on the ground surface (sand usually moves within one meter of the ground surface).
(iii) Abrasion: Wind erodes by sandblasting.
(iv) Desert Pavement: Stony surface veneer (thin layer) composed of particles that are too large to be moved by wind—deflation removes fine particles and the remaining large particles are leveled by sandblasting.
(b) Wind Deposits:
(i) Loess: Extensive blankets of wind-blown silt from desert silt or from "rock flour" from stratified glacial drift.
(ii) Sand Dunes: Sand accumulations develop wherever an obstruction blocks the wind. Sand accumulation next becomes its own self-made wind obstruction. Dunes tell us about: wind direction, variability of wind, availability of sand supply, presence of vegetation.
C) Landforms Created by Glacial Erosion
Glacial Trough: Deepened, straightened, "U"-shaped valley that was once occupied by a glacier.
Hanging Valley: Valleys of tributary glaciers, which are left standing above the main glacial valley.
Cirque: A hollowed-out, bowl-shaped depression which has 3 steep walls but is open down-valley.
Horn: A sharp peak at the intersection between numerous cirques.
Arête: A sharp bedrock ridge between 2 glaciers.
Fjord: Glacial trough that is submerged by rising sea level.