Chapter 18: Glaciers and Ice Ages Flashcards
sublimate
to evaporate (from snowflake form) directly into vapor
firn
deeply buried snow that transforms into a packed granular material
glacier
a stream or sheet of recrystallized ice that stays mostly frozen all year long and flows under the influence of gravity.
Mountain Glaciers
aka alpine glaciers; exist in or adjacent to mountainous regions if temperatures remain cold enough. Flow from higher elevations to lower elevations. Include cirques, valley glaciers, ice caps, and piedmont glaciers.
cirque glaciers
fill bowl-shaped depressions (cirques) on the flank of a mountain
valley glaciers
rivers of ice that flow down valleys
ice caps
mounds of ice that submerge peaks and ridges at the crest of a mountain range
piedmont glaciers
fans or lobes of ice that form where a valley glacier emerges from a valley and spreads out in to the adjacent plain.
Continental glaciers
vast ice sheets that spread over thousands os square kilometers of continental crust. Today these only exist in Antarctica and Greenland, and rest mostly on solid ground
how do glaciers move?
through plastic deformation (the process where existing grains of ice slowly change shape without breaking or new grains grow while old ones disappear); this occurs at the deeper part of the glacier (below the brittle plastic transition depth)
crevasse
a crack that opens into a downward tapering gash (occurs higher in the glacier; above the brittle plastic transition)
basal sliding
when a glacier glides along on a wet sediment slurry without coming into frictinal contact with bedrock and as a consequence, may undergo a surge
surge
when a glacier moves faster than normal
ablation
the removal of ice by melting, sublimation (vaporizing directly), and calving (breaking off chunks)
zone of accumulation
where snowfall adds to the glaciers mass
equilibrium line
the boundary between the zone of ablation and the zone of accumulation
glacial advance
when the rate at which ice builds up in the zone of accumulation exceeds the rate at which ablation occurs, then the glacial toe move forward into previously unglaciated regions (position of the toe move downslope in this case)
glacial retreat
when the rate at which ablation occurs exceeds the rate at which ice builds up in the zone of accumulation (toe moves back toward the origin of the glacier)
tidewater glaciers
glaciers whose toes lie in the sea water; valley glaciers entering the sea become ice tongues (longer than they are wide); continental glaciers entering the sea are known as ice shelves
sea ice
occurs where the surface of the sea itself freezes; not technically glacial ice
glacial incorporation
when ice surrounds loose rock and carries it away
glacial plucking
occurs when ice flows into joints that intersect the bedrocks surface. Freezing and thawing, along with the push of moving ice, causes joints to grow until a joint-bounded block of rock finally breaks free of its substrate and starts to move with the ice.
glacial abrasion
as glaciers flow, sand and silt embedded in the ice act like the teeth of a giant rasp and grind away the substrate
glacial striations
where clasts moving with the glacial ice carved grooves or scratches into bedrock
tarn
a lake formed at the point where the head (source of a glacier) once existed
arete
a residual knife-edge ridge of rock, separates two adjacent cirques
V-shaped valley
formed by a river channel
U-shaped valley
forms because the combined processes of glacial abrasion and plucking not only lower the floor of the valley, but also erode its sides.
hanging valleys
where a glacier cuts the floor of its valley down to a depth that far exceeds the depth cut by the tributary glaciers. consequently, when the glaciers melt away, the mouths of the tributary valleys perch at a higher elevation than the floor of the trunk valleys (waterfalls)
truncated spurs
where trunk glaciers remove the ends of ridges between valleys
rouche moutonnee; sheep rock
glacially eroded hills
fjord
a glacially carved valley that has filled with water; occur in Norway, New Zealand, Chile, Alaska, and Greenland
- marine fjords/coastal fjords (occur along the coast and fill with seawater)
- freshwater fjords (inland lakes)
moriane
a pile of sediment either carried on or left behind by a glacier
lateral moraine
sediment dropped on the side margins of a glacier (bathtub rings)
medial moraine
a stripe down the interior of the composite glacier (where two valley glaciers might come together, their meet would form this type of moraine
ground moraine
sediment left at the base of the glacier when it melts away
end moraine
sediment transported to a glaciers toe and accumulates there
glacial drift
the several different types of sediment that can be deposited in glacial environments. Includes:
- glacial till
- glacial erratics
- glacial marine
- glacial outwash
- loess
- glacial lake-bed sediment
glacial till
sediment transported by ice and deposited beneath, at the side, or at the toe of a glacier moraine; not sorted
glacial erratics
relatively large cobbles and boulders that have been dropped by a glacier, can be in till or on a glacially polished surface
glacial marine
clasts carried out to sea by icebergs, when the ice melts the clasts sink to the sea floor
loess
forms from clay and silt that were transported by strong katabatic winds
glacial lake-bed sediment
fine grained sediment, including rock flour, that accumulates on the floor of a meltwater lake; contains varves
varves
a pair of thin layers deposited during a single year; one layer of silt brought in with spring floods, and a clay layer deposited in winter when the lakes surface freezes over and water is still
terminal moraine
the end moraine at the farthest limit of glaciation
recessional moraine
an end moraine that forms when a glacier stalls temporarily while receding
drumlins
from the Gaelic word for small hill or ridge, flowing glacial ice reshapes the underlying till into elongate hills
kettle holes
form when till covered blocks of ice calve off the toe of a glacier; when the blocks melt, the depressions form
knob and kettle topography
land surfaces spotted with many kettle holes separated by rounded hills or ridges of sediment
esker
sediment deposited in meltwater tunnels beneath a glacier as a sinuous ridge after the glacier has melted away
glacial outwash plains
braided meltwater streams that flow beyond the end of a glacier deposit layers of sand and gravel
ice-margin lake
meltwater may collect in a lake adjacent to the glaciers toe
glacial subsidence
when a large ice sheet grows on a continent, its weight causes the surface of the lithosphere to sink
post glacial rebound
when a large ice sheet melts, gradually, the surface of the underlying continental lithosphere rises back up
glacial torrent
erosion caused by glaciers that results in an ice dam or moraine dam suddenly breaking, yielding an immense flood
pluvial lakes
lakes that accumulated to the south of continental ice sheets due to enhance rainfall
permafrost
permanently frozen ground
paleosols
ancient soil preserved in the stratigraphic record
glaciation vs. interglaciation
glaciation: an ice age
interglaciation: the time between an ice age
tillites
ancient glacial deposits that have hardened into rock.
