Earth Science Exam 2: Glaciers

Where and why do glaciers form?

• Cold climates - cold enough for snow to last year after year, allowing it to accumulate, compact into ice, and slowly flow under gravity

What are accumulations? How does it relate to advance or retreat of terminus?

• winter snowfall > summer melt

• snow accumulates over years

• deeper layers compressed & recrystallized as glacier ice

• ice flows towards terminus

What is an ablation? How does it relate to advance or retreat of terminus?

• melting (of ice to water)

• iceberg- calving (if terminus is in water)

What is a mass balance? How does it relate to advance or retreat of terminus?

• positive mass balance if accumulation > ablation (terminus advances) 

• negative mass balance if accumulate < ablation (terminus retreats) 

What is a cirque glacier?

• a small glacier near mountain top

What is a valley glacier?

• long glacier flowing down valley(s)

What is an ice field?

• central ice area with outflow to multiple glaciers

What is a Piedmont glacier? 

• broad ice lobe on lowland 

What is basal sliding?

glacier sliding over its bed

what is internal deformation?

plastic flow of ice under stress

what is subglacial deformation?

movement of soft sediments beneath the glacier

what is a fracture flow?

movement caused by ice breaking in steep areas 

What is glacier abrasion?

• scraping of bedrock by sediment in basal ice; akin to sandpaper

What is glacier plucking?

• freezing of bedrock blocks into basal ice; faster erosion than abrasion

What are cirques?

• small bowl-shapes valley eroded by cirque glacier; landform left after glacier melts

What are glacial troughs? 

• U-shaped valley eroded by valley glacier

What are horns?

• sharp mountain bedrock ridge left by nearby glacial erosion 

What are aerates?

• sharp bedrock ridge left by nearby glacial erosion 

What are laterals?

• ridge of sediment at side of glacier

What are medials?

• ridge of sediment in middle of glacier; from where two lateral moraines join

What are end moraine?

• ridge of sediment at end of glacier; outermost = terminal moraine 

What is an outwash plain? 

• flat sand & gravel deposit beyond glacier; deposited by braided rivers 

What are drumlins?

• streamlined hill; elongated parallel to ice flow; more elongated if faster ice flow

What are eskers?

• sinus sand & gravel ridge; deposit of meltwater river in tunnel in ice sheet

What are kames?

• mound of sand & gravel 

What are kettles? 

• pond or small lake, due to melting of buried ice 

About how thick are the modern Greenland and Antarctic ice sheets?

• 3 km thick

• 4.8 km thick

What type of glacier covered New York State at the Last Glacial Maximum (LGM) and what is the evidence for its thickness & extent?

• continental ice sheet; thick and vast covering millions of square kilometers

• moraine, till deposits, striated bedrock, erratic boulders, drumlins, eskers, and isostatic depression

How was sea level different at the Last Glacial Maximum (LGM)?

• 120-130 meters lower than today b/c much of the water was trapped in massive ice sheets

What causes glacial-interglacial cycles over tens of thousands of years? 

• changes in the earths orbit and tilt alter how much sunlight reaches the planet, causing ice sheets to grow or shrink