Glaciation Flashcards
Pleistocene
The epoch (period) that dated from 2 million years ago to 11,500 years, the early part of the quaternary which included the most recent ice age.
What is the Pleistocene regarded as?
a single ice age - but there were multiple periods of glacial (stadial) and interglacial (interstadial) conditions - periods fluctuated.
Long term causes of climate change:
The Milankovitch cycles:
- Eccentricity of the orbit
- axial tilt
- wobble
Short term causes of climate change:
- solar forcing (sunspots)
- volcanic eruption
Eccentricity of the orbit (orbital stretch) + what it causes
- when the orbit of the earth changes from nearly circular to elliptical over a period of 100,000 years - changes the amount of radiation the earth receives (circular = colder periods, elliptical = warmer periods)
Axial tilt
- when the tilt of the earth varies from 21.8 - 24.4 degrees over 41,000 year cycle.
- The greater the tilt is towards the Sun, the more solar energy the poles recieve = favours interglacial periods (+ favours glacial when tilting away.
Wobble
- wobbles in a circular motion + changes the point in the year where the Earth is closest to the Sun (axial precession) over a 21,000 year cycle - causes changes to when different seasons occur.
Holocene (interglacial)
is the period we now live in
Quaternary period
Started 2 million years ago and is what we are in today.
What are the milankovitch cycles sustained by?
Climate feedback mechanisms - positive and negative feedback.
Positive feedback
AMPLIFY change - e.g. cold temp is sustained by increased snow cover (increases surface albedo.)
Negative feedback
DIMINISH change - e.g. increase in temp = increase in evaporation of ocean surface water = increase in low thick cloud cover - this counteracts warming as it reflects solar energy to space.
what is solar forcing? what happens when there is a lot of it? + background info
The more sunspots on the Sun’s surface, the more solar energy will be emitted, the earths global temp will increase.
- 20% of the 20th century warming was caused by solar output variation.
- But - total variation in solar radiation caused by sunspots is only 0.1% - solar forcing is a contributing factor to climate change.
Effects of volcanic eruptions
- can increase and decrease global temp
- volcanoes with high VEI eject huge volumes of ash, sulphuric dioxide, CO2, and water vapour - which high level winds distribute around the earth.
Ash and sulphuric acid aerosols reflect solar radiation back into space, causing a global cooling effect, which can last from months to years.
CO2 - enhance greenhouse effect + has a warming effect.
Cryosphere
The parts of the Earth’s crust and atmosphere subject to temps below 0 for at least part of the year.
Ice sheet
a broad, thick sheet of ice covering an extensive area for a long period of time.
Ice cap
Dome shaped mass of glacier ice found in upland areas (smaller version of an ice sheet.)
Ice field
Thinner ice covering an upland area (formed by ice caps connecting.)
Cirque valley
Smaller glacier in a hollow of a mountain side.
Valley glaciers
Glacier confined between valley walls.
Permafrost
soil and rock that remains frozen if temps do not exceed 0 in the summer months for at least 2 consecutive years.
Talik
soil within permafrost (unfrozen ground)
The types of permafrost + explanation of what they are.
- Continuous - continuous sheet of frozen ice
- Discontinuous - areas of permafrost interspersed with talik.
Sporadic - larger area of talik vs permafrost
Active layer
The top layer of soil in permafrost environments that thaws during summer (producing meltwater which saturates upper layer due to permafrost being impermeable = meltwater causes distinctive periglacial landscapes to be created!) And freezes during winter.
Name all the periglacial processes:
- Nivation
- Frost heave
- freeze thaw weathering
- solifluction
- meltwater erosion
- wind action
Nivation
is a combinaton of processes that weakens and erodes the ground beneath a snow patch, which forms a nivation hollow. - these processes include freeze thaw weathering, solifluction and meltwater erosion.
Frost heave
The freezing and expansion of soil water causes the dislocation of soil and rocks. As the ground freezes, large stones become chilled faster than the soil, the water below the stone’s freezes + expands, causing the stones to be pushed upwards + forming small domes on the ground surface.
Freeze-thaw weathering
when water seeps into the cracks of rocks and then freezes + expands (up to 10%) weakening the rock through repeated freeze-thaw cycles, eventually causing the chunks of rock to break away.
Solifluction
is the slow downhill flow of saturated soil – the active layer provides enough water to allow flow to occur, this forms solifluction lobes.
Wind action
- Due to lack of vegetation and plentiful loose material, allows strong cold winds to pick up large amounts of material and redeposit it far away from its source as loess E.g., in the Mississippi-Missouri Valley, USA.
Meltwater erosion
During the short summer, thawing creates meltwater, which erodes river channels, refreezing at the onset of winter causes a reduction in discharge and sediment deposition in the channel.
Where are periglacial landscapes found?
at the fringes of polar glacial environments + dominated by permafrost.
simple solar forcing (changes in solar output) effects + how long effects last.
The changes in the amount of energy emitted from the sun due to the number + density of sunspots - 11 year cycle + can last 100 - 150 years.
Simple volcanic eruptions effects + how long effects last.
eruptions with high VEI = eject huge amounts of ash sulfur dioxide + CO2 into atmosphere = cooler temps globally as ash reflects solar radiation back into space - lasts 1 - 2 years.
Ablation
The output of snow and ice from a glacier by melting, calving of icebergs, sublimation or evaporation.
Plucking
Occurs where rocks are weakened or well-jointed and where there is meltwater present at the base of the glacier. The meltwater penetrates into joints and around obstacles then freezes onto the rock. As the ice moved, it exerts an immense pulling force onto the attached rock, which is plucked from its position. Also known as quarrying.
Entrainment
The process by which surface sediment is incorporated into a fluid flows (e.g. ice) as part of the process of erosion.
Supraglacial
Debris transported on the surface of the glacier
subglacial
debris transported beneath the glacier
Englacial
Debris transported inside the glacier.
