Glaciated landscapes and glaciers of the past Flashcards
What are past ice masses due to?
Sea level rise
What was sea level like 16,000 years ago?
120 m lower than it is today
What can past measures be used to do?
Predict future levels- speed and extent of sea level rise
What type of response is not ideal?
A non-linear response
What can ice masses that are no longer here give information about?
See how quickly they disappear and if there is evidence of non-linear behaviour which can be applied to Greenland and Antarctica as there were ice sheets over Europe and America in the past
Why is it important that we have knowledge of past glaciers in terms of their glacier bed?
To see its flow and how they impact on the landscape
What are the 3 types of Milankovitch cycles?
Eccentricity
Obliquity
Precession
How long do glacials last?
90,000 years
How long do interglacials last?
10,000 years
How long does eccentricity last?
100,000 years
What is eccentricity?
How elpitical the earth’s orbit is
What is obliquity?
The tilt of the Earth’s axis
How long are obliquity cycles?
41,000 years
What is precession?
The wobble of the Earth on its axis
How long do precession cycles last?
27,000 years
What do the Milankovitch cycles affect?
How much radiation the Earth receives
Which Milankovitch cycle affects interglacial cycles?
Eccentricity
Which Milankovitch cycle is the weakest?
Eccentricity
When did these Milankovitch cycles take place?
During the quaternary
How many cycles have there been in the quaternary?
21 glacial-interglacial cycles
What is at the end of the quaternary?
The holocene
What is the holocene?
The current interglacial
How long has the holocene lasted so far?
12,000 years so its a bit long
When was the last glacial period?
100-12 ka
What was the last glacial called?
Weichselian
When was the last glacial maximum?
26-18 ka
What was the ice like in the last glacial period?
It was much more extensive covering N America, N Europe
Where was the Laurentide ice sheet?
Over N America and Canada
Where was one of the big ice streams on the Laurentide?
Hudson Bay
What did the Hudson Bay ice stream do?
Discharge icebergs into the North Atlantic every 7000 years
What does IRD stand for?
Ice-rafted debris
How was IRD found?
Through ice cores
What is IRD?
Debris that are too big to be carried by ocean currents and are instead transported by icebergs. This gets deposited when the iceberg melts
How many layers of IRD have been found?
About 6
What are these events of iceberg discharge called?
Heinrich events
What is the periodicity of Heinrich events?
7.2 ka
What is surprising about these Heinrich events at the Laurentide ice sheet?
They occurred during relatively cold periods
What is the binge phase?
This is where as much ice is accumulated as possible
What are stadials?
Short periods of cold
What are interstadials?
Short warm events
During what period (interstadial or stadial) did Heinrich events occur?
Stadial
What is the purge phase?
Loss of ice
Sediment thaws resulting in rapid movement and therefore iceberg lost
What happens if there is lots of thick ice?
The base of the ice melts
How much water did Hudson Bay release over 250 years?
2.3 million km3
What is the binge-purge theory?
Binging phase causes ice to build up
Ice underneath melts
Causes a purge
What is another theory about Hudson Bay Heinrich events?
Global cooling
Explain the global cooling theory
Ice accumulated as a result of global cooling.
As it grew, icebergs had to remove some ice
What are two issues with the global cooling theory?
Never explains why the cooling happened
No explanation of time frame
What is the external forcing and isostatic uplift theory?
The Laurentide advanced in cooling periods, then ocean warming flooded in and caused iceberg discharge, now there is less ice so the pressure underneath is not as much, causing the ice to move up and cut off the warm water supply
What is the evidence for external forcing and isostatic uplift theory?
From one ice core, far away from the site
Reliability?
What have Heinrich events shown?
The non-linear response to climate
What was the name of the last interglacial?
Eemian
When was the last interglacial?
115,000-130,000 BP
What was the mean temp. of Eemian?
Mean temps 1 degrees C warmer
1.5 in certain places
Was the Greenland ice sheet bigger or smaller in the last interglacial?
It was smaller
What was the sea level like in the last interglacial?
5-7m higher
What was the CO2 concentration like in the last interglacial?
Much lower
What was found under Trafalgar Square?
Animal remains from animals you would expect to see in Africa- must have been warmer in the past
What are glacial landforms created by?
Glacial deposition or glacial erosion
What are two forms of glacial erosion?
Abrasion
Plucking
What is abrasion?
Glacier has rock stuck in the bottom and scrape out the landscape
What is plucking related to?
Basal sliding
What is plucking?
Ice under high pressure melts, water flows round the rock and refreezes onto the top of the rock but as it is still moving downhill it rips the rock away
Where can glaciers move material?
Over the top at the surface
Through the bottom on the bed
Within the glacier
Where is most glacial deposition seen?
At the margins of the glacier
What do the characteristics of the deposited material depend upon?
Source e.g the atmosphere/ glacier bed
Route e.g supraglacially
Where it is deposited
Is supraglacially moved material severely modified?
No, it is barely modified
What happens to subglacial material?
It becomes very modified
What do glaciers deposit?
Till
Diamtic
What is till?
A generic name
What is diamtic
Material that is definitely known to be from a glacier
What are the characteristics of till?
Heterogeneous grain size
Large clasts, silt and clay matrix
Unsorted pebbly mud
What is a terminal moraine?
A moraine that marks the extent of the glacier
What information do moraines give?
Ice extent in the past
Retreat pattern of glaciers that exist- can tell the speed of retreat and other info
What are lateral moraines?
Moraines at the side of glaicers
What do lateral moraines tell us?
The area and height of the glacier
What do drumlins have?
A steep front and long tail at the end
Which side of the drumlin is upstream?
The steep side
What do drumlins show?
The flow characteristics
What are fast flow features important for?
The stability of the glacier
What are mega scale glacier lineations?
They are essentially bigger versions of drumlins
How do we know that drumlins and mega scale glacier lineations give information about glaciers?
They are found at areas of recent glaciation
What do eskers relate to?
Subglacial hydrology
What are eskers?
Casts of subglacial channels
What is needed for eskers to form?
Lots of water
What are eskers an indication of?
An ice margin that was retreating rapidly
What are P forms?
Erosional froms of eskers
How are P forms formed?
They are scraped out of the rock by water under high pressure which erodes the rock
What scale are U shaped valleys?
Landscape scale
What is the theory of Gamburtsev Mountains, why haven’t they changed?
They are seen as the birth place of East Antarctica. Theory is that the ice grew really quickly and encased the mountains
What happened to the English-Irish ice sheet at the start of the interglacial?
It retreated very quickly
What is the bedrock responsible for?
Difference in the bedrock topography caused a difference in the response of the glacier to climate change.
The bedrock topography is to do with the history of the glaciers
How are ice cores sampled?
Drill into the centre of the ice sheet to avoid deformation of the ice core
What do the layers show in ice cores?
Accumulation, then melt then accumulation the next year to give layers over each year
What can be used to date ice cores?
Tephrachronology
What is special about tephra?
It has a unique fingerprint
What happens to the annual layer thickness as the depth of the ice core increases?
As the depth gets deeper, annual layer thickness decreases
What are the records like for Greenland?
Shorter time scale but higher resolution
What are the records like for Antarctica?
Longer time scale but smaller resolution
How deep can the ice cores be collected in Greenland?
3000m
How many years ago can we get ice cores in Greenland for?
123,000 years ago
How deep can the ice cores be collected in Antarctica?
3000m
How many years ago can we get ice cores in Antarctica for?
800,000 years
What is a key thing that ice cores can tell us?
Atmosphere at that time (gaps between the snow trap the atmosphere in bubbles)
What do ice cores allow comparison of?
Atmosphere and ice volume which can be linked
What can ice cores show changes of?
Pollution and ice flow
Why does a cage need to be put up?
In case of electrical storm
