glaciers chpt. 14
Positive and negative budgets result in? Glaciers having a balanced budget have a? Most glaciers are in retreat b/c? A persistent negative budget result in?
"advance & retreat" of the terminus stationary terminus global warming the disappearance of a glacier
besides melting, glaciers also _______?
"sublimate", where ice converts directly to water vapor
Glacial Budget-
a glacier's behavior depends on the balance b/w accumulation & wastage (melting)
Erosion by Valley Glaciers -Horns:
a pyramid-shaped peak left when headword erosion happens by at least 3 glaciers in same peak
glacial flow velocity increases _________________ in the _______ zone, but __________ in the zone of _________.
down slope in the accumulation zone, decreases in zone of wastage.
The Milankovitch Theory -3 primary factors -claimed that: -proposed: 1 2
-orbital eccentricity, changes in axial tilt, percussion of the equinoxes -irregularities in earth's rotation and orbit; bring climate changes. An explanation for the onset of glacial episodes 1- "Variations in solar energy" -due to solar flares or interstellar dust 2- "Volcanic eruptions" -cause short term change.
Erosion by Valley Glaciers -Cirques:
@ upper part of glacial trough, a scoop-shaped depression, eroded into a mountain side marks the place where glacier formed & moved out into a trough
Glacial Drift - 2 types of drift:
Till- sediments deposited directly by glacial ice; sorted poorly Stratified drift- sediments deposited by running meltwater, in braided streams; well-sorted.
which of the following cross-valley profile is typical of canyons & valleys eroded and deepened by alpine or valley glaciers?
U
Erosion by Valley Glaciers are _ shaped erosion
U-shaped glacial troughs valley glaciers carve angular peaks & deep valleys or rounded valley floors/ vertical valley walls
mountain river valleys usually have a _ shaped profile a FIORD forms when
V-shaped sea level rises, fills U-shaped glacial valley w/ water
Glaciers are - part of the hydrologic cycle
a "RESERVOIR" where water is stored for long periods from ocean-2-land-2-oceans
most continental glaciers flow at only ________?
a few cm to m per day b/c they are @ high latitudes, usually frozen to their underlying surfaces & basal slip is minimal
Landforms composed of till -Recessional moraine:
a glacier reaches its 'maximum extent' & has a balanced budget, it deposits a "terminal moraine" if has 'negative budget'-- its terminus retreats, "deposits ground moraine" in this case another end moraine is deposited but called "recessional moraine"
Rocks and sediments in glaciers
abrade (scrape off) underlying rocks & grind them into a fine powder called "ROCK FLOUR"
valley glacier that lengthens (extends its terminus downslope) over a period of many yrs applies to?
accumulation exceeds wastage
a glaciers budget is balanced when:
additions to the zone of accumulation equal losses in the zone of wastage
Continental Glaciers and Erosional Landforms -areas eroded by 'continental glaciers':
are smooth & rounded, ice-sourced plains. create deranged drainages w/ swamps & lakes -exhibit large areas of polished & strained bedrock
icebergs-
aren't glaciers b/c they float in water & not on land
if slope is present, glaciers slide over their underlying surface thru?
basal slip melt-water helps to lubricate basal slip
what are the 2 major flow mechanisms in a glacier?
basal slip and plastic flow
glaciers _____ loose materials in their paths erode by 'abrasion'- erode by 'plucking'-
bulldoze the movement of sediment-laden ice over rock surfaces when ice freezes in r around bedrock projections & pulls them loose
Deposits in Glacial Lakes -Varves:
couplets of dark & light, laminated, fine-grained sediment. 1. dark layers- made of clay & organic matter, form during winter 2. lighter layers- made of slit & clay, form in warmer months
Erosion by Valley Glaciers -Hanging valleys:
create waterfalls form when the floor of a former glacial tributary is higher than the main valley
Landforms Composed of Till -End moraines:
crescent shaped deposits of till that form near the terminus of the glacier. are elongated ridges "form as a pile of rubble @ the end front of the glacier"
ice is a ____? fresh snowflakes are about ____? order of snowflakes
crystalline solid 80% air glacial ice -->firn-->granular snow-->snowflakes
How fast do glaciers move?
depends on slope, discharge, and season. valley glaciers move FASTER than continental glaciers
Landforms composed of till -Ground moraines:
deposits of till left by a retreating glacier have irregular, rolling topography
Glaciers do what to large amounts of sediments b/c they are?
erode, transport, & deposit b/c they are moving solids
snowfields-
exist yr round in some mountains, but b/c they don't move, they aren't glaciers
abrasion also results in ________?
glacial striations- scratches made by rocks scraping against each other as glacier moves
how do glaciers originate and move?
glaciers form when winter snowfall exceeds summer melt & snow accumulates yearly
Kinds of Glaciers -Valley Glaciers what are tidewater glaciers?
in high mountain ranges. long, narrow tongues of ice, smaller than cont. glaciers. flow from higher to lower often have tributaries also called "Alpine" glaciers valley glaciers that flow into the sea
In a cross-section of a glacier, where do the greatest flow velocities occur?
in the few tens of meters above the base
Erosion by Valley Glaciers -Arete:
is a serrated ridge b/w U-shaped glacial troughs or b/w adjacent criques
Glaciers are
masses of ice that move over land by plastic flow & basal slip 2.15% of all water on earth, 10% land surface
most of glaciers movement is?
plastic flow, a type of deformation that takes place in response to stress
which of the following is laid down by a retreating glacier?
recessional moraine
Landforms composed of till -Lateral and Medial Moraines:
ridge shaped deposits of till that from w/in glacier -- created by plucking rock from the valley walls Lateral moraines- form along sides of glaciers Medial moraine- form where 2 lateral moraines meet
Landforms composed of stratified drift -Outwash plains: -Valley trains:
sediments deposited by "glacial meltwater; well-sorted" outwash plains- blankets of sediment, sand & gravel, that form in front of glacier as it melts valley trains- deposits of braided streams form long, narrow deposits of stratified drift
Pleistocene Glaciations: the little ice age:
series of "ice ages" & warmer intervals that occurred 2.6 million to 10,000 yrs ago colder winters & short, wet summers
Ice caps-
similar to cont. glaciers but smaller some develop from valley glaciers often develop in flat areas, such as Iceland & Alaska
firn forms when?
snow thaws and refreezes becoming granular
Landforms composed of till -Drumlins:
streamlines hills of till shaped by Continental glaciers or by glacial meltwater floods. may contain 100s of them
glaciers only exist where there is: these conditions are in:
sufficient snow fall, summer temps low enough to delay melting high mountains high latitudes (Alaska, Canadian Arctic islands, Greenland, & Antartica)
Glacial Drift- erratics-
term for all glacial deposits huge boulders made from distant source areas, transported to current location by glaciers
Glacial buget -firn limit:
the line separating the 2 zones shifts at least somewhat each yr
Glacial budget -zone of wastage:
the lower part, where losses from melting, sublimation, & calving of icebergs exceed grains
which of the following best describes the term glacial drift?
the sedimentary materials outwash & till
Glacial budget -zone of accumulation
the upper part of the glacier where snow cover is yr-round
how do glaciers move?
through "BASAL SLIP" & "PLASTIC FLOW"
Kinds of glaciers -Continental Glaciers (ice sheets)
unconfined by topography & flow outward in all directions from a zone of accumulation found in Antartica & Greenland
a glacier that is confined by topography & has tributaries is a:
valley glacier
glacial ice forms when?
when firn is buried, it recrystallizes (metamorphoses) to "glacial ice" & flow under its own weight
