Glacial Erosion and Deposition
Objectives
• Introduce glaciers as important agents of
landscape formation, and discuss the different
categories of glaciers
• • Give a brief overview of how past glaciation
has influenced Earth’s surface over large areas of
the continents
• • Describe the formation of glacier ice and its
movement through the glacial system
• • Explain how glaciers shape the landscape
through erosion and deposition
Glaciers
• Cryosphere
– All forms of frozen water
– Snow, icebergs, ice sheets, and glaciers
• Glacier
– Body of ice formed on land and in motion
Glaciers
• Mountain (Alpine)
Glaciers
– Cirque glaciers confined to
hollows below mountain
peaks
– Valley glaciers fill deep
troughs carved into
mountains
• Continental Glaciers (Ice
sheets)
– Large landmasses covered
with sheets of ice
Glaciers of the Past
• Glacial periods
– Ice sheet expansion in
high to middle latitudes
– Due to cooling climatic
conditions
• Deglaciation
– Glacial retreat due to
warming climate
conditions
• Interglacial
– Warm period between
glacial periods
Formation of Glacier Ice
• Begins with snow
– Summer snow loss is
less than winter gain
– Compacted snow
– Recrystallized by
melting and refreezing
of ice in pore spaces
• Firn
– Granular, compacted
snow
– Not quite glacial ice
• Glacial ice
– Further compression
and recrystallization
Ice Accumulation and Ablation
• Zone of Accumulation
– The addition of snow
• Zone of Ablation
– Loss of ice
• Melting – phase change of a
solid to a liquid
• Sublimation – phase change
of a solid to a gas
• Calving – break up of
glaciers that flow into ocean
Glacial Movement
• Glacial Surge
– Rapid movement as much
as 1 m/hr
• Glacial Creep
– Internal deformation of ice
• Glacial Sliding
– Movement of the entire
glacier over the rocks below
Glacial Movement and Temperature
• Warm weather
– Glaciers generally retreat
– Ice at or near melting
point
– Melt water moves to the
base
– Produces basal slip
• Cooler weather
– Glaciers grow
– Ice below freezing point
– Temperatures rise toward
base
– Produces glacial creep
Glacial Erosion
• Plucking
– Bedrock is broken off and frozen
within a glacier
• Abrasion
– Rock debris carried by glaciers
scrapes the bedrock below
• Striations
– Linear gouges caused by rock
debris within glaciers scratching
the bedrock
• Roche Moutonnee
– Asymmetrical mounds caused by
abrasion on one side and
plucking on the leeward side