Theme 8: Glacial systems Flashcards
What causes the sea level to change?
the exchange of water stored on land as glaciers and ice caps with ocean water. This plays a major role in global water balance.
What is glaciation? Deglaciation? Interglaciation? Ice age?
Glaciation: The period during which continental ice sheets grow and spread outward over vast areas.
Deglaciation: When the climate warms or snowfall decreases, ice sheets become thinner and cover less area. Eventually, the ice sheets may melt completely.
Interglaciation: A period following deglaciation, but before the next glaciation period. Climate is mild.
Ice age: A succession of alternating glaciations and interglaciations, spanning a period of millions of years or more
What is the most influential cause of the quaternary glaciations? We are in a… (BOF)
Astronomical factors involving the Earth’s rotational and orbital patterns changed the amount of solar radiation.
Eccentricity - the shape of the Earth’s orbit (ellipsoid)
Obliquity - tilt angle of the Earth’s axis relative to the Sun
Precession - toll movement around the Earth’s axis
We’re in an interglacial period, because the previous glaciation was the Wisconsinan glaciation.
What does ice sheet growth and flow cause?
Glaciers cause isostatic depression due to their weight and fore bulge of the lithosphere at their edges. Once they disappear, we see isostatic rebound.
They are dynamic as they flow in all directions.
SEE SLIDE ON THIS
What is a glacier? How does it form? Where do they form? What conditions are needed?
Glacier = mass of ice formed by the accumulation and crystallization of snow. A glacier moves (flows) under the influence of its own mass and gravity. (Defining criteria: a glacier is derived from snow and flows)
They form where cool air temperatures and snowfall permit the accumulation of snow over years. More snow has to fall and accumulate in the winter than melts in the summer.
This can happen in the Arctic where temperatures are cold and summers are so short that most of the winter snowfall is preserved.
It can also occur at progressively lower latitudes (but at higher elevations) where snowfalls are so great that even warm summers do not cause complete melt.
How does ice evolve in a glacier?
Each layer of snow is an annual accumulation. With time, snowflakes become rounded due to the compression of overlying layers and crystallization. This causes us to have, from bottom to top: glacial ice, firm snow, fresh snow.
Describe the mass balance of a glacier? (Accumulation zone, ablation zone, equilibrium line)
Accumulation zone = where accumulation > ablation. Here material is added, and no mass is lost. This zone changes every year, but it is located in the upper parts of the glacier.
Ablation zone = area of a glacier where more mass is lost than gained. It’s a process of removing material from a glacier/ice sheet. It is located in the lower part of a glacier where the ablation is greater than the accumulation.
Equilibrium line: ACC zone = ABL zone
Terminus: ABL=ACC+Flow
Name all the glacier types and how they are classified
Glaciers that are unconfined by topography (biggest to smallest):
ice sheets (the largest),
ice shelves (on the ocean) and
ice caps (like ice sheets only smaller).
Glaciers that are confined by topography – mainly valley glaciers (biggest to smallest):
niche glaciers
cirque glaciers
valley glaciers
Glaciers that are non-confined by topography:
Outlet glacier: Where an ice stream from an ice cap flows into a valley (sometimes flowing into the sea)
Piedmont glacier: Where a glacier flows from a valley into an open plain (where it tends to fan out because it loses confinement of the valley).
Describe ice sheet dynamics and name important features
Glaciers have two distinct zones:
(1) the Accumulation zone refers to inputs of snow
(2) the Ablation zone refers to losses of snow
Crevasses: deep open cracks in the ice, reflecting accelerating flow or steps in the terrain below the glacier
What deposits are left by ice sheets?
Marginal landforms
Step 1: ice sheet present. With the ice front stabilized and the ice in a wasting, stagnant condition, various depositional features are built by meltwater
Step 2: The ice has wasted completely away, exposing a variety of new landforms made under the ice
Glacial drift: includes all rock debris deposited in close association with glaciers. There are two major types:
Stratified drift: layers of sorted and stratified sediments (clays, silt, sand and gravel), deposited by meltwater streams or bodies of water adjacent to the ice.
Till: an unstratified mixture of rock fragments, ranging in size (from clays to boulders), deposited directly from the ice without water transport. It forms a sequence of ice-contact landforms: including moraines, drumlins and till plains
What is erosion made by ice sheets called?
Glacial action abrades the rock into a smooth form as it rides over the rock summit, then plucks bedrock blacks from the lee side, producing a steep, rocky slope
Glacial erosion: Slow movement of the glacier causes curving and shaping of the land beneath the moving glacier
Two main processes of glacial erosion:
- Abrasion: occurs when particles scrape against each other
- Plucking: Erosion and transport of large chunks of rocks. Water seeps into cracks in and/or around the rock fragments. Rock becomes unstable, picked up and eroded.
What are alpine glaciers?
Alpine glaciers = glaciers found in mountainous areas.
Glaciers are sensitive to changes in air temperature which currently is causing them to shrink due to atmospheric warming. (Mass balance is negative, more ablation than accumulation)
What is a moraine? What are the different types of moraines?
Moraine = material (sediment) left behind by a moving glacier
End moraine - a ridge of till that forms at the terminus of a stationary glacier
Recessional moraine - a series of end moraines formed by a receding glacier that periodically stabilized.
Terminal moraine - the last recessional moraine representing the point of farthest glacier advance
Lateral moraine - only produced by valley glaciers, these are ridges of till paralleling the valley walls, deposited at the margins of the glacier. Sediment is abraded and plucked from valley walls and mass wasted onto the glacier surface
Medial moraine - central moraine formed when two valley glaciers merge and combine their lateral moraines
Ablation moraine - a sheet of till that is deposited as glaciers stagnate and then gradually down waste
What is an esker? Kettles? Drumlins? Kames?
Eskers - steep-walled, sinuous ridge of sand and coarse-grained stratified material deposited by streams of meltwater which flow in tunnels within or beneath the ice.
Kettles - circular depressions formed by the melting of buried ice. If they contain water, they’re kettle ponds/lakes.
Drumlin - produced by continental glaciers, these are smooth, elongate, parallel hills of reworked glacial till that are thought to form when glaciers advance over previously deposited drift. The steep sides face the direction of advance.
Kames - steep sided conical hills of stratified drift that collected in openings or lakes in the ice sheets. After the ice melts, they remain.
In a glaciated landscape, what is a lacustrine deposit? What about an outwash plain?
Lacustrine (lake) deposits – varve layers deposited by standing water.
Varves: Pairs of coarse- and fine-grained material (light and dark colored) sediment beds deposited in a single year in glacial lakes.
Outwash plains - area beyond the margins of glacier where meltwater (as braided streams) deposits sand, gravel, and mud washed out from the melting ice
