Geography Reference
In-Depth Information
Finally, protection involves engineering solutions such as tidal bar-
riers with large sluice gates on estuaries to prevent very high tides
from entering the estuary. The challenges for coastal management
are enormous because the system is dynamic requiring flows of
sediment, water and energy. Interfering with those flows in one
place has knock-on effects further along the coast. Some coastal
areas are currently responding most to short-term changes caused
by human action whereas others are still responding to changes in
sea level since the retreat of ice sheets began at the end of the last
glacial period some 18,000 years ago.
ICE
Ice exists on Earth today mainly in large ice sheets over the Ant-
arctic and Greenland, in ice caps, in sea-ice over the North Pole
and in valley glaciers on land. It also exists in large quantities within
frozen ground known as
permafrost
and produces characteristic
landforms in cold regions. If the amount of ice present today in the
Greenland ice sheet melted this would raise sea levels around the
world by 5 metres. Ice sheets form over very large areas, the size of
continents, and are typically a few kilometres thick. Ice sheets flow
slowly although there can be faster moving rivers of ice within
them. In Antarctica the faster moving ice streams feed
ice shelves
which are formations of floating ice which then melt into the
ocean or are broken away and float off into the ocean.
Glacier and ice sheet dynamics
Glaciers are much smaller than ice sheets, covering individual
valleys on land but they occur on every continent. Glaciers are
formed in mountainous regions wherever snow accumulates at a
faster rate than it can be melted. This therefore requires both a
good supply of precipitation and cold conditions. A typical glacier
has an accumulation zone at the top where rates of gain are more
than losses and an
ablation zone
at the bottom where rates of loss
are greater than rates of gain. The loss of ice at the outlet of the
glacier mainly occurs through melt water but sometimes, if the
glacier directly flows into the sea, icebergs can be broken off and
float away before melting.
