Transcript BLAKENEY ESKER - British Geological Survey

CLIMATE CHANGE
In Norfolk
Jökulsarlon, Iceland
© NERC 2005, AM Jarrow
Introduction
• Norfolk’s location and low lying coast
– vulnerable to climatic changes
• Natural glacial-interglacial cycles for
last 2.6 million years (Quaternary)
• Not a recent trend caused by us
• But humans are having an affect too
North Norfolk
• Quaternary (2.6 million years ago to
present)
– interglacial stages (warmer)
• warmer than present - Costa del Cromer
– glacial stages (colder)
• like present day Antarctica
• These climatic changes have affected
Norfolk’s coastline and appearance
Norfolk during glacial stages
• During a glacial stage
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glaciers grow around the world
take water from the seas
lower global sea levels
coastline moves outwards
Norfolk increases in size
• If glaciers grow and reach Norfolk
– glaciers cover Norfolk and change the land’s
appearance
During interglacial stages
• Opposite during interglacials
– global sea levels rise
• No solid high cliffs to keep sea out
– coastline migrates inland
• To simplify the Quaternary we will
split it into two…
2.6 million years ago to
900,000 years ago
• Coastline further inland (sea levels)
• S England joined to France
– creating a land bridge
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Warmer climate
Small oscillations
Small sea-level changes
Ever-changing coastline
© NERC 2006, JR Lee
2.6 million years ago to
900,000 years ago
• Landscape similar to today
– saltmarshes, tidal creeks, estuaries,
beeches
– sands, gravels and muds laid down during
this time are called ‘crags’ by geologists
An ancient beach deposit at Norton
Subcourse in southern Norfolk. These
sands and gravels are called the
Wroxham Crag.
© NERC 2005, JR Lee
900,000 years ago to
present
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A large climatic shift occurred
Climate dominated by extremes
Global, not just felt in Norfolk
About 10 shifts from glacial to
interglacial
• Several identified in geology of
Norfolk
900,000 years ago to
present
• Several occasions – Norfolk covered
by ice or near ice margin
• At maximum extent – British Ice
Sheet reached London.
– about450,000 years ago
– known as the Anglian Glaciation
How Norfolk changed
• Each of the glaciations had a dramatic
affect on Norfolk
– glaciers smear sediment on land surface
• Sediment laid down by glacier in this way
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geologists call this deposit Till
usually clayey, also some sand and gravel
depends on what glacier is ‘carrying’
depends on which rocks ice has travelled over
• Reason many fields in Norfolk are clayey
How Norfolk changed
• When the glaciers retreat
northwards due to global warming
– water released from the ice
– lots of sand and gravel carried by water
– this is deposited as water slows down
• Reason there are many sandy fields
and quarries/pits in Norfolk
Layer cake
• Geologists think of Norfolk as a cake
with many layers
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till
sands and Gravels
till
etc…
The cliffs at Happisburgh, showing deposits laid down
during a glaciation. Two tills are separated and overlain
by sands that were deposited within a glacial lake.
© NERC 2005, JR Lee
Coastline variations
• These large-scale climate changes =
large-scale changes in sea level
– change of several 10s of metres
© NERC 2006, JR Lee
Rivers
• River pathways affected by glaciations
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glaciations erode and bury earlier landscapes
change direction of river drainage
can destroy whole river systems
glaciers melt and drainage of the meltwater
uses old river pathways
– modern day drainage network is based on
ancient drainage pattern
Drivers of climate change
Fjallsjokull, Iceland
© NERC 2005, AM Jarrow
Drivers of climate change 1
1. Distribution of land and water on
the Earth
–
thermohaline circulation
Drivers of climate change 2
2. Solar radiation
• orbital shape or
eccentricity
• axial tilt or obliquity
• axial orientation or
precession
© NERC 2006, JR Lee
Climate change record
Present
2.6 million years ago
© NERC 2006, JR Lee