Glaciers (chapter 11 in Summerfield)

• Permanent (on human timescales) body of ice, consisting largely of recrystallized snow, that shows evidence of downslope or outward movement due to pull of gravity.

• ~10% of surface of continents covered by ice today, but ~30% covered as little as ~18,000 years ago (landforms, sediments, isostasy, climate records)

• Glaciers responsible for huge amounts of erosion in high-elevation terrain (although processes tough to observe, poorly understood)

Glaciers (chapter 11 in Summerfield)

• Form depends on competition between accumulation and melting of ice

• Snow accumulates and compacts to form ice, but ice doesn’t sit still… it deforms plastically

(handout)

Crevasse

Types of glaciers

(1) Temperate vs. Polar

(2) Alpine or mountain glaciers• Valley glaciers• Cirque glaciers• Fjord glaciers

Ice caps or ice sheets or continental glaciers• Today, only Greenland and Antarctica• Their combined mass is 95% of ice on Earth• Melt would cause 200 ft sea level rise• Can have ice shelves (floating ice at coast)

Small scale erosional features: Glacial striations & polish

Glacial Erosion

CirqueGlacial Erosion

Cirque

Cirque

Glacial Erosion

Cirque: North CascadesGlacial Erosion

Fjords, Greenlandorth CascadesGlacial Erosion

U-shaped valley, hanging valleysGlacial Erosion

Arete North CascadesGlacial Erosion

HornNorth CascadesGlacial Erosion

Glacial Deposits

Till: unsorted glacial sediment

Glacial Deposits

Yeager Rock, a 400 ton erratic on the Waterville Plateau, Washington

Glacial Deposits

Lateral moraine, Switzerland

Glacial Deposits

Lateral moraine, Switzerland

Glacial Deposits

Dropstones: Ice-rafted glacial debris

Glacial Deposits

Glacial outwash - sediment choked streams from melting glacier form braided streams, deposit poorly sorted, stratified sediment

Iceland

Esker: long, winding ridge of stratified sand and gravel

Why????

Esker: long, winding ridge of stratified sand and gravel

Why????

Drumlin

Glacial landforms

DrumlinsGlacial Erosion

Glacial landforms

Kettle lakes: depressions under glacier remain after glacier melts

Siberia

Puget Map Glacial Landscape

J Harlan Bretz and the Channeled Scablands

What processes link climate change, glaciers & sea level?

Eastern Juan de Fuca Strait was filled with ice prior to 13,000 years ago (13 ka). The area was isostatically depressed.

When climate warmed and the ice melted ~12 ka, how did local RELATIVE SEA LEVEL change?

time

local sea level

Relative sea level curve, Juan de Fuca Strait (Mosher et al., 2004) Global eustatic sea level curves (Fairbanks, 1989; Peltier, 2002)

Relative sea level curve, Juan de Fuca Strait (Mosher et al., 2004)

Rapid isostatic rebound causes local relativesea level to drop rapidly

As rebound slows, effect of global (eustatic) sea level rise wins out, causing local sea level rise