Glaciers

Glaciers of the past...

+1821-Idea that glaciers were bigger in the past suggested by Ignaz Venetz +1836-Confirmed by Louis Agassiz in the Alps +1900s-By this time scientists realized that glaciers had grown and retreated several times

Milankovitch Cycles

+3 Cycles -Eccentricity -Obliquity -Precession +3 cycles work together to cause Earth's ice sheets to shrink and expand every 20,000 years +Also cause some glacial periods to be more or less intense

Greenland ice sheet

+80% of the island covered by ice +Average thickness=5000 ft, but it reaches 10,000 ft thick in places

Fjord

+A glacial trough that occurs along the coast and has been flooded with ocean water

How fast do glaciers move?

+Average velocities vary +Fast - 2 meters per day +Slow - Trees and vegetation can grown on the glacier

Snowline

+Boundary between the Zone of Accumulation and Ablation

Outwash Plain

+Broad layer in which stratified drift is deposited +Pockmarked with kettles

Obliquity

+Changes in the tilt of Earth's axis -Tilt today - 23.5 degrees -Varies between 22 and 24.5 degrees

What are the effects of glaciers?

+Climate Changes +Forces migration of animals and plants +Changes in stream courses +Worldwide change in sea level +Crustal Subsidence

Kettles

+Depressions or lakes found in outwash plains +Form when chunks of ice break off of the glacier -Sediment is deposited around the ice, and the ice later melts, leaving behind a hole in the sediment

Precession

+Earth's axis traces out a circle in the sky -Today, the axis points to the North Star, but that changes over time -This also causes seasons to switch places about every 10,000 years

Small changes in Earth's orbit

+Earth's orbit changes slightly -This affects how much sunlight the Earth receives +Referred to as Milankovitch Cycles

Eccentricity

+Earth's orbit is sometimes more or less circular

Types of Moraines

+End Moraine +Lateral Moraine +Medial Moraine +Ground Moraine

Ice Sheets

+Exist on larger scale than valley glaciers +Cover huge areas +Completely bury landscape below

Valley (alpine) Glaciers

+Form in the mountains +Form in valleys that had originally been carved out by streams

Ice Shelves

+Form where ice sheet glaciers flow into the ocean +Ice floats on the ocean, but is still connected to land -Cover huge areas -Ross Ice Shelf is the size of Texas by itself

Ice Age

+Glacial and interglacial periods part of a larger Ice Age +Ice Age began between 2 and 3 million years ago when ice sheet glaciers became established in the northern hemisphere -The ice sheet glacier over Antarctica has probably been tere for at least the past 14 million years

Glacial Erosion

+Glacials effective at eroding rock -Weigh a lot; can pick up and carry away all sizes of sediment

Plucking

+Glacier rip up chunks of rock

Plate Tectonics

+Glaciers only form on land, so land needs to be located near the poles for ice to grow on

Changes in Stream Courses

+Great Lakes did not exist pre-Ice Age +Missouri River drained -> Hudson Bay instead of Mississippi River +Other rivers currently flowing into Mississippi once flowed into the Atlantic Ocean

Where are two major ice sheets on Earth?

+Greenland + Antarctica +These ice sheets combined cover nearly 10% of the Earth's area

Basal Slip

+Ice not attached to the ground and slips and slides along under its great weight

Where do glaciers form?

+In areas where more snow falls in winter than melts during the summer

Aretes

+Knife-edge ridges carved between two alpine glaciers

Paternoster Lakes

+Lakes in glacial troughs that were created when the glacier plucked and scoured the valley bottom

Crevasses

+Large cracks

Ground Moraine

+Layer of till deposited as an alpine or ice sheet glacier melts

Moraines

+Layers or ridges in which till is deposited +Produced by both alpine and ice sheet glaciers

Till

+Material deposited directly by the ice +Glaciers drop till as they melt +Made up of all sizes, from clay particles to large boulders +Deposited in Moraines

Plastic Flow

+Occurs below depths of 150 feet +Ice is under high pressure and bends/flows like taffy or caramel

Horns

+Occurs when glaciers cut back into mountain peaks, making them sharper

Zone of Accumulation

+Part of the glacier that does not melt in the summer

Zone of Ablation

+Part of the glacier that melts away in summer

Glacials

+Periods when Earth's glaciers grew +Last glacial period ended about 12,000 years ago

Interglacials

+Periods when the ice retreated, like today

End Moraine

+Pile of debris deposited at the end of a glacier +Alpine and Ice Sheet glaciers

Lateral Moraine

+Pile of till deposited along the edges of an alpine glacier

Medial Moraine

+Pile of till deposited between two alpine glaciers that have flowed together

How do glaciers move?

+Plastic flow +Brittle flow +Basal slip

What causes glaciations?

+Plate Tectonics +Small changes in Earth's orbit -First suggested by Milutan Milankovitch

How do glaciers erode?

+Plucking +Abrasion

Abrasion

+Rocks within the ice acting like sandpaper to smooth and polish the surface below

Worldwide change in sea level

+Sea level was 330 ft lower than today

Drift

+Sediment deposited by a glacier +Two types -Till -Stratified drift

Stratified Drift

+Sediments deposited by melt water (water flowing from the glacier) +Typically well-sorted (grain sizes are all about the same) due to water separating them out -Mostly made of sand and gravel +Typically layered +Deposited in an Outwash Plain

Hanging Valleys

+Small glacial troughs left behind from tributary glaciers that flow into a main glacier -Not as deep as the main valley left behind by the main glacier -Up above the main valley; rivers flowing through the valley usually create spectacular waterfalls

Climate Changes

+Southwest US was wet +Many large pluvial lakes existed

How do alpine glaciers affect the landscape?

+Tend to make the landscape more rugged and dramatic

How do ice sheet glaciers affect the landscape?

+Tend to plane off the landscape -Wisconsin

Glacial Striations

+The grooves carved out of the rock below a glacier with chunks of rock at its bottom that drag along the bedrock -Useful to determine direction of glacial movement

Crustal Subsidence

+The weight of glaciers caused the continents in the northern hemisphere to sink down into the mantle

Glacier

+This mass of ice +Occurs on land +Forms from the accumulation, compaction, and recrystallization of snow

How many zones are glaciers divided into?

+Two -Zone of accumulation -Zone of ablation

Glacial trough

+U-Shaped valley carved by a glacier

Antarctic ice sheet

+Up to 14,000 ft thick

Brittle Flow

+Upper 150 feet of the ice is not under enough pressure to flow like taffy +As the ice below flows it breaks and pulls apart the ice above to form large cracks or crevasses

Types of Glaciers

+Valley (alpine) Glaciers +Ice Sheets +Ice Shelves

Glacial Erratics

+Very large boulders of a rock type different from the bedrock below glaciers +Typically polished and scratched, as a result of being dragged by the glacier