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