Glaciers and Glacial Landforms

Glaciers and Glacial Landforms

• Glaciers are large masses of compressed ice, accumulating over years of snowfall, and moving under their own weight.
• Ocean ice is not considered a glacier.
• Glaciers form in high elevations (alpine glaciers) or near polar ice caps (continental ice sheets).
• Alpine glaciers can form near the equator if located at high enough elevations.
• Continental ice sheets (Greenland, Antarctica) are very thick and depress the land beneath them.
• Glaciers move downhill or outward via plastic flow (like silly putty) or sliding on meltwater.
• Plastic flow is slower at the edges due to friction, faster in the center.
• Glacier movement rates vary, from a few meters per year to 100 meters/day (surging glaciers).
• Erosion, weathering, and deposition are all involved in glacial landform creation

Glacier Movement and Types

• Valley glaciers carve U-shaped valleys extending from high elevations.
• Ice fields are glaciers filling the area between peaks.
• Tidewater glaciers meet the ocean.
• Piedmont glaciers extend onto flat land, not the ocean.
• Glacier movement depends on accumulation (snow gain) and ablation (snow loss).
• Advancing glaciers are growing; retreating glaciers are shrinking.
• Glaciers are constantly moving outward, like conveyor belts

Glacial Weathering and Erosion

• Glaciers weather and erode rocks through frost wedging (water freezing expands cracks) and abrasion (rock fragments grind surfaces).
• Glaciers transport weathered rock fragments, pushing and dropping them (deposition).
• Glacial deposits (poorly sorted) are characterized by angular grains of all sizes (from mud to boulders)

Glacial Landforms

• Moraines: piles of glacial sediment (lateral, terminal, ground, medial).
• Glacial erratics: large, isolated rocks left by glaciers.
• Drumlins: mounds shaped by advancing glaciers over ground moraines.
• Outwash plains: plains of sediment deposited by meltwater in front of glaciers.
• Eskers: raised river beds carved by meltwater beneath glaciers, visible after retreat.
• U-shaped valleys: glaciers carve valleys with steep sides.
• Cirques: bowl-shaped depressions carved at the top of glacial valleys.
• Hanging valleys: smaller tributary valleys that "hang" above the main valley below.
• Arêtes: thin, sharp ridges carved between parallel valleys.
• Horns: sharp peaks formed where multiple cirques meet.
• Fjords: U-shaped valleys flooded with seawater.

Glacial Impacts and Cycles

• Glaciers cover roughly 10% of Earth's land surface today and 30% during the last ice age.
• Evidence of past glaciation includes moraines, striations, lake sediments.
• Ice ages are periods when glaciers advance, while interglacials are periods of retreat.
• Ice ages are influenced by small changes in Earth's tilt, solar energy, greenhouse gases, and ocean currents.
• Greenhouse gases like water vapor, CO2 and methane trap heat in the Earth's atmosphere.
• Increased levels of greenhouse gases lead to warmer temperatures, while decreased levels lead to colder temperatures.
• Glaciers' retreat and advance affect sea levels, climate zones, and agriculture.

Mass Movement

• Mass movement (mass wasting or landslides) is the downhill movement of soil or rock due to gravity.
• Water doesn't drive mass movement. Fluvial processes involve water, aeolian involve wind.
• Water can intensify mass movement, such as in debris flows or hyper-concentrated flows.
• Landslides are a general term; geologists use specific classifications.
• Landslides are categorized by material type, motion type, and motion rate.
• Gravity is the driving force.
• The angle of repose is the critical angle where material slides.
• Slope stability is influenced by factors like weathering, water, human activities (e.g., road construction), and geological structure.
• Types of motion include: falls (e.g., bedrock falling); slides (rotational, translational); flows (chaotic, fluid-like).
• Debris flows are a type of mass movement with a mixture of water, mud, and boulders.
• Mudflows are a subset of flows, involving finer materials.
• Avalanches involve dry material (snow or rock).
• Subsidence occurs when ground collapses from support removal (e.g., water erosion, groundwater pumping).
• Sinkholes are a common example of subsidence.
• Lahars are volcanic mudflows.
• Understanding mass movement is critical for risk mitigation.