Download Information Sheet D7

CLIMATE CHANGE
The action of ice
Information
Sheet No
Glaciers
14
Glaciers are rivers of ice that move down-slope,
usually from highlands or mountainous areas,
to the sea. They are important agents of erosion,
transportation and deposition. They have played
a major role in shaping the landscape of the
Burren, and much of the Northern Hemisphere
that was covered by ice during the last Ice Age
(>12,000 years ago).
Glaciers form when winter snowfall exceeds
summer ice melt. This can happen within a
fraction of a degree Celsius - and so glaciers are
very sensitive indicators of changes in climate.
Since 1850, when scientific monitoring of
the world’s glaciers began, many glaciers are
retreating consistently decade by decade.
The total surface area of glaciers on Earth
has decreased by 50% since 1850. This
phenomenon is affecting glaciers at all latitudes
and longitudes and has been attributed to global
warming. The process has increased dramatically
since 1995.
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Glacier
Water
Glacier Margin
June 19th, 2005
July 7th, 2003
May 12th, 2001
Retreat of the Helheim Glacier, Greenland
(2005, 2003, 2001)
Grosser Glacier, Switzerland
The most significant global effect of glacial
retreat is a rise in global sea levels. The current
projected rise in sea level due to glacial retreat
is 0.27 to 0.5 m by 2050, and 0.8 to 1.3 m
by 2100; this is considered by many to be a
conservative estimate. Cities that would face
serious flooding include London, New Orleans,
Shanghai, Rio de Janeiro, Buenos Aires, Cairo,
Mumbai, Tokyo, Lagos, Bangkok, New York
and Los Angeles. The total population living in
low-lying areas at risk is 640 million people.
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CLIMATE CHANGE
The action of ice
Information
Sheet No
The Burren during the last ice age
15
Approximately 1.8 million years ago, an ice age
began during which most of Ireland was covered
by glaciers. The last stage of this ice age ended
12,000 years ago.
Some rocks at the base of the ice sheet were
pushed along under the weight of the ice and
as they moved they scratched the underlying
bedrock. When you examine the flat surface of
the bedrock at several localities in the Burren, you
will see such scratches, known as glacial striations.
If you put a compass along the line of the
scratches you can see that they are facing in a
WNW-ESE direction. You can therefore assume
that the ice moved in this direction.
Looking west towards Black Head
As the glaciers moved from southwest County
Galway over the Burren they smoothed the
north-facing slopes of the Burren’s hills. This
is clearly visible on the smooth slopes of Black
Head. The glaciers also removed weathered
shale rocks from the land’s surface; plucked
blocks of limestone from the south-facing slopes
of the hills and left scratches (striations) on the
exposed limestone bedrock.
As the ice sheets moved over the Burren,
they bulldozed and eroded the surface of the
underlying rock. The moving ice carried along
with it all the loose sediments, shattered stones,
rocks and boulders that it picked up along its
route.
Terrain map of the
Burren, showing
the direction of
movement of the most
recent ice sheets.
Striations on limestone bedrock
When the temperature warmed up and the
ice began to melt much of this material was
dropped or deposited on the landscape.
Deposited glacial material includes erratics,
glacial till (up to 20 m thick in some valleys),
drumlins and moraines.
Like the glacial striations, the drumlins and
moraines indicate the path taken by some of
the most recent ice sheets as they moved from
southwest County Galway over north Clare. They
moved from the north-east and westwards out over
the Atlantic Ocean, as indicated in the map below.
CLIMATE CHANGE
The action of ice
Information
Sheet No
Glacial deposits in the Burren
16
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When the temperature increased approximately
12,000 years ago, the last ice age ended. As
the ice melted it dropped its load of sediment,
rocks and stones. This load was dropped in
different ways and created different features
on the landscape which are still visible today.
Common glacial depositional features on the
Burren include erratics, glacial till, drumlins and
moraines.
Erratics
Erratics are pieces of rock that have been
transported from their original location by
moving ice, and were deposited when the ice
melted. The most obvious erratics in the Burren
are those that are several metres wide, but there
are also many smaller, pebble- or cobble-sized
erratics.
Limestone erratic in the Burren
Some erratics in the Burren appear raised off
the adjacent pavement on what are called
“pedestals”. These pedestals show that the
pavement surrounding the erratics has been
lowered by dissolution since the last glaciation,
but the pavement underneath the erratic has
been protected from the rain and has not been
lowered. The height of the pedestals allows us to
calculate how fast the limestone surface is being
lowered by dissolution - 1 cm every 1,000 years.
This means the hills of the Burren will disappear
in less than 3 million years!
Erratics being exposed at the edge of a glacier in
Canada as the ice melts
Most erratics in the Burren region are of
limestone, and so came from the Burren itself.
There are, however, erratics of other rock types:
granite erratics are common along the north
coast of the Burren and sandstone erratics are
scattered throughout the area. The nearest source
of granite is the Galway granite to the north.
This tells us that the ice sheets that passed over
the Burren came from the north. The sandstone
erratics could have come from Slieve Aughty
mountains to the east, or from the erosion of the
delta sandstones that once covered the Burren.
Erratics occur at up to 200 m above sea level in
the Burren region, indicating that the ice sheet
that covered the area was at least a couple of
hundred metres thick.
Granite erratic on the Flagg y Shore
Granite
Limestone
Siltstone/
shale
Sandstone
Geological map of the area
A
Drumlins
Drumlins are small, low, rounded hills that
make the landscape look like a gently rolling
blanket. These low hills were formed at the
end of the last Ice Age when the great ice
sheets that covered Ireland were melting. These
features were first recognised in Ireland; the
word drumlin comes from the Irish “droimnín”
or “small hill”. The drumlins are not made of
rock - instead, they are made of till - mixed-up
deposits of boulders, pebbles, and soil. They are
rounded in shape because they were moulded or
streamlined as the ice moved over them.
B
C
D
E
Drumlin in the Burren (Turlough Valley)
F
G
nd)
Glacial till (Aughinish Isla
A: Limestone erratic at Poulnabrone
B: Ice shattered limestone erratic in Burren
National Park
C: Granite erratic at Doolin Point
D: Conglomerate erratic at Lough Bunny
E: Limestone erratic at Doolin Point
F: Granite erratic at Lough Bunny
G: Granite erratic at Flaggy Shore
CLIMATE CHANGE
The action of ice
Information
Sheet No
Melting ice and sea level change
17
Background
Contrary to common perception, the melting of
floating sea ice does not affect global sea levels.
Ice has a lower density than water and so melts
to a smaller volume. Therefore the melting
of sea ice and icebergs will not contribute to
rising sea levels. If, however, continental ice
sheets melt, global sea levels could rise by many
metres and much of today’s continents could
be flooded. The melting of sea ice can lead
to melting of continental ice. If sea ice melts,
less sunlight will be reflected from the Earth’s
surface and the oceans will warm, eventually
raising temperatures enough for continental
ice sheets to melt. If this happens, there will
be a huge increase in the amount of freshwater
entering the oceans. This will reduce the salinity
of the world’s oceans and affect ocean current
patterns.
As ocean currents transfer heat from warm
areas to colder parts of the world (e.g. the Gulf
Stream), a change or shutdown of these currents
will result in severe cooling in many parts of the
world.
Before undertaking the following activity,
participants should be aware that (1) there are
large ice caps on Greenland and Antarctica; and
(2) water expands as it freezes (and so water
takes up less space than ice)
Activity Material:
• Two 500ml vessels (e.g. glass beaker)
• One tin of beans/peas ( to act as the
continents)
• Two rulers
• Warm water
• Ice cubes
• Blu-tak
• student worksheets
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Activity:
Part One:
Introduce the fact that much of the Arctic
Ocean is frozen and so are the seas around
Antarctica. This activity investigates if there will
be a change in sea level if floating sea-ice melts..
To set up the experiment for “sea ice” melting:
• Participants fill one 500 ml vessel roughly
half-way with warm water.
• Crushed ice is added to raise the water
level by 1 or 2 centimetres. The crushed ice
imitates floating sea ice.
• With a ruler participants measure and
record the level of water in the beaker
• When the ice has melted completely, the
level of water is measured and recorded
again.
Part Two:
Introduce the fact that Antarctica and
Greenland are covered by ice up to 3 km thick
in places. This activity investigates how melting
land ice could affect global sea level.
To set up the experiment for “land ice” melting:
• Participants place a tin of beans in the
centre a vessel. The vessel is then filled with
water to a level close to the lid of the tin.
(The tin represents the continents)
• With a ruler participants measure and
record the level of water in the beaker
• Crushed ice is placed on top of the tin of
beans. (The crushed ice imitates continental
ice sheets, such as on Greenland).
• When the ice has melted completely, the
level of water is measured and recorded
again.
Participants can record their results on the
worksheet.