Glaciation Flashcards
Define stadial and interstadial
Stadial: Short-lived colder periods within a major glacial, associated with ice advance.
Interstadial: Short-lived warmer periods within a major glacial, associated with ice retreat.
What is a key factor in determining whether we enter a glacial period?
The amount of solar radiation received during the summer months as this will determine whether ice built up over the winter will stay or melt.
What is an example of an unconstrained ice mass?
Ice sheets, ice caps, ice streams.
Where are periglacial landscapes found?
At the edge of permanent ice.
What are the processes operating in periglacial landscapes?
nivation, frost heave, freeze-thaw weathering, solifluction, ground contraction, high wind, meltwater erosion, groundwater freezing.
What is dynamic equilibrium?
Rates of accumulation match rates of ablation.
What is the difference between pressure melting points of temperate and polar glaciers?
-PMP in temperate glaciers are more consistent with depth, whereas PMP in polar glaciers increases with depth.
-PMP is higher in temperate glaciers than in polar glaciers.
What is one example of a meso-scale landform?
Roche moutenées, crag and tail, drumlins, meltwater channels, eskers, moraines.
describe the process of plucking.
plucking occurs when basal meltwater freezes around part of the bedrock at the base of the glacier. Any loosened rock fragments are plucked away as the glacier moves forward.
Where does medial moraine form?
At the intersection of two joining glaciers.
periglacial processes-nivation
a combination of processes weakens and erodes the ground beneath a snow patch including freeze-thaw weathering, solifluction and meltwater erosion.
periglacial processes-frost heave
the freezing and expansion of soil water creates pore ice or ice needles. this causes the upward dislocation of soil and rocks. As the ground freezes, large stones become chilled more rapidly than the soil. water below these stones freezes and expands, pushing these stones upwards
periglacial processes-freeze-thaw weathering
when water freezes in the cracks and joints of rocks, it expands. this exerts stresses within the rock, enlarging cracks and pores. eventually large chunks of rock break away.
periglacial processes-solifluction
the downslope movement of the saturated active layer under the influence of gravity
periglacial processes-ground contraction
when dry areas of the active layer refreeze, the ground contracts and cracks. meltwater enters the cracks during the summer and will then freeze in the winter
periglacial processes-high wind
a lack of vegetation cover means the wind is able to pick up large amounts of material and redeposit it far away.
periglacial processes-meltwater erosion
during the summer, thawing creates meltwater which erodes stream or river channels. refreezing in winter causes sediment deposition in the channel
periglacial processes-groundwater freezing
when water is able to filter down into the upper layers of the ground and then freeze, the expansion of the ice causes the overlying sediments to heave upwards into a dome.
periglacial landforms-patterned ground
repeated freezing and thawing of moist, frost-susceptible soil forming circles, polygons, irregular nets and stripes.
periglacial landforms-ice wedges
vertical masses of ice that penetrate down to 10 metres from the surface in some cases. formed as a result of meltwater entering a ground crack in the summer and freezing when the temperature drops. causes an expansion which fractures the surrounding material and makes the wedge deeper and wider. during the intense cold of winter, the surrounding soil contracts which creates a gap between the developing ice wedge and adjacent soil where more water can infill. this process will continue over time and the ice wedge will continue to widen and deepen
periglacial landforms-blockfields
extensive areas of angular rock that have been created by regular freeze-thaw activity. the material is left strewn across the level ground with blocks representing more homogenous lithology and the gaps where the bedrock had more weaknesses and/or joints. large areas of these rocks are called felsenmeer- where this occurs on rock faces on a gradient, scree will be left at the bottom of the slope where talus accumulates.
periglacial landforms- pingos
hills with an ice core. they are between 3 to 70 metres in height and circular in shape. the ice in the centre accumulates because of hydrostatic pressure or groundwater flow