Jkulhlaups:

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Jökulhlaups
Hemis Number 161760 2GS333 Geohazard Management
and Remediation

• Glacial Lake Hazards

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What is a Jökulhlaup

• Jökulhlaup is icelandic for Glacier Floods
• Otherwise they are known around the world as
  Glacial Lake Hazards
• Or Glacial Outburst Floods

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Where Do They Occur?

• They can occur anywhere which has glaciers on
  volcanoes or in a volcanic region
• Areas of mountains with high rainfall
• Usually in High Altitude regions at low Latitudes

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Examples of Locations

• The Cascades USA
• Wisconsin USA
• Grimsvötn Iceland
• Himalayas Nepal, Bhutan
• Andes - Peru

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How They Are Formed Glacial Lakes

• Glaciers Lakes occur when glaciers form due to
  snow and ice not melting from one year to another
  and being compacted by more ice and snow.
• The Lake is meltwater build up at the most down
  valley point of a glacier
• The meltwater material is dammed in by Moraine
  deposits

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How They are Formed Subglacial Lakes

• Subglacial Lakes are formed by geothermal warming
  the base of a glacier and forming a lake under
  the glacier
• The shape is formed by an equilibrium of vertical
  forces, as the overlying glacier floats in static
  equilibrium
• The roof of the lake slopes about 10 times
  steeper then the glacier in the opposite
  direction

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Subglacial Lakes

• The diagrams opposite show how the lakes change
  with the affect of magma upwelling
• The top picture is a stable lake
• The Bottom is unstable

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How They Fail Glacial Lakes

• Glacial Lakes Fail by breaking the Moraine Dam
• The failure can occur by heavy rainfall over a
  short period of time, leading to the lake to
  increase in size and putting to much pressure on
  the dam
• The failure can occur from general glacier
  retreat allowing meltwater to enter the lake and
  increase pressure on the dam
• A third failure is through an avalanche or
  landslide into the lake causing a wave to over
  top the dam

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How They Fail Subglacial Lakes

• Jökulhlaups occur when meltwaters drains from a
  sub-glacial lake
• This can be done by melting of ice walls due to
  friction and heat
• Or the Lake levels lifts the ice dam and the
  glacier flows on the water
• They can escape through or under the glacier

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Effects

• Sediment 3.8107m3 Moves through an event
• 108 of material moves in a violent volcanic
  eruption
• Have been known to discharge at 60000m3/sec
• Run out distances of 200km have been recorded

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Effects

• Although the events rarely cause many casualties
  it causes major economic and communication damage
  in poorer remote regions of countries
• This becomes more of a problem especially if the
  country is already poor

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Geomorphology Changes

• No 2 Jökulhlaups are the same, this is due to the
  major change they cause to a valley system and
  flood plain
• They can transport large boulders and icebergs
  along its course
• The quaternary glacial outburst produced the
  areas of the world know as Scablands such as
  the one in North America
• They also produce Kettle-holes, giant current
  ripple marks

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A map of the North American scablands
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Geomorphology Changes - Evidence
Top left shows Ripple Marks Top Right shows
erratic blokes Bottom Left Shows Debris (with the
front left bloke being 5foot high
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Monitoring

• Due to the number of glacial lake outbursts and
  Jökulhlaup and the locations of the events it is
  not cost affective to try and stop the hazard to
  occurring
• It is more cost effective and easier to manage
  and mitigate against the problem

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Monitoring

• The monitoring of these lakes is predominately
  done with Remote Sensing
• Remote Sensing allows the glaciers which are
  inaccessible to be monitored for predicting an
  event.
• Also a number of research groups have started up
  to work with the vulnerable governments on
  monitoring and remediation techniques

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Monitoring

• monitoring of seismic activity can lead to
  predictions of volcanic activity and thus the
  possibility of a Jökulhlaup event
• In Iceland monitoring of the glacial lakes water
  chemistry has become important, as it is now
  noted that the lake has an increase in Sulphur
  before a Jökulhlaup occurring

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Remediation Techniques

• Remediation techniques in Nepal includes the
  removal of water from the major hazards
• The Tsho Rolpa Glacial Lake has grown from
  0.23Km2 to 1.7Km2 since 1950
• Its water level has dropped 3m since remediation
  work started
• But another 20m needs to be removed before being
  deemed safe

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Mitigation

• If people are under immediate danger from a
  Glacial Lake Outburst Flood, they are warned by a
  siren or emergency radio messages
• The use of canals to remove water from the
  Glacial Lakes

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CASE STUDY

• Volcanic origin
• ICELAND

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Grímsvötn Iceland

• 10 of Iceland is ice-covered
• 60 of the ice covers active volcanic zones
• There has been 10 major subglacial volcanic
  eruptions in the 20th century and 5 minor ones in
  the same period
• The Vatnajökull glacier is the largest
  continental glacier in Europe
• With Grímsvötn being the largest subglacial lake
  in Iceland.

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Grímsvötn Iceland

• The Glacier covers a hydrothermal area as well as
  a 10km wide and 300m deep depression
• The extent of the lake is identified by a flat
  ice shelf with abrupt change in surface slope at
  the margins
• This lake was profiled by using radio echoing and
  seismic profiling
• The lake is inside the caldera and with the south
  and west mountain walls blocking the lake by not
  being covered by the glacier

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Grímsvötn Iceland

• Grímsvötn Volcano lies under the Vatnajökull
  Glacier in the South East of Iceland next to
  Skaftafell National Park
• These region of Iceland is very remote but has
  major communication links across it

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Grímsvötn Iceland
G
Map of Iceland showing the volcanoes and ice caps
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Grímsvötn Iceland
Map of the Vatnajökull glacier, showing Grímsvötn
volcano
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Grímsvötn Iceland

• Grímsvötn is a Caldera at an elevation height of
  1725m
• The centre of the volcano is 50km from its
  Northern edge and 45km from its Western edge, it
  has 35km2 of Ice fills the caldera
• The Caldera produces the most number of sub
  glacial eruptions than any other volcano in the
  world
• The caldera has erupted nearly 50 times since its
  first eruption in 1332

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Grímsvötn Iceland

• However not all eruptions produce Jökulhlaups
• The 15 subglacial eruptions during the 20th
  century was about 33 of all icelandic eruptions
  of the 20th Century
• It is depended on how much water is under the
  glacier
• If the meltwater under the glacier is high enough
  it will cause the ice dam to be lifted off the
  caldera and thus a flood to occur
• Most of the eruptions produce partial melting of
  the glacier

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Grímsvötn Iceland

• Time Scale
• 4th November 1996 2130
• High frequency constant tremors recorded at
  Grímsfjall station.
• These tremors are the wrong frequency to be
  landslide, volcano or earthquake.
• The amplitude of the tremors increased from 3-5
  units at first recording to 120 units at 7am on
  the 5th.

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Grímsvötn Iceland

• Time Scale
• 5th November 1996 10am
• Fast growth of the Jökulhlaup estismated speeds
  reached 6000m3/sec
• The road across Skeiðarársandur was closed.
• A 900m long bridge spanning the River Skeiðará
  was surrounded
• Icebergs were being broken off the front of the
  glacier and taken down the river
• The amplitude of the tremors now reached 160
  units

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Grímsvötn Iceland

• Time Scale
• 5th November 1996 1pm
• The bridge across the glacier river Gígjukvísl
  had been destroyed in the flood
• Power lines and telephone lines cut
• 5th November 1996 6pm
• The Bridge across Sæluhúsakvísl destroyed
• Flow rate estimated at 25000m3/sec
• 10million worth bridge spanning Skeiðará is
  severely damaged

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Grímsvötn Iceland

• Time Scale
• 6th November 1996 9am
• The Jökulhlaup reached speeds of 45000m3/sec
• Bridges across Sæluhúsakvísl and Gígjukvísl
  washed away, while 200m of the Skeiðará bridge
  was washed away
• Icebergs up to 200 tonnes in weight scattered
  across the alluvial plane
• 7th November 1996 Midnight
• Jökulhlaup has ended.
• 400m3/sec is the flow rate in the rivers
• Estimated 3km3 of water, ash and other debris
  washed out to sea since the start of the event

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Grímsvötn Iceland

• Despite the size of the flood caused by the
  volcanic activity there was only 0.4Km3 of
  volcanic material emitted

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Grímsvötn Iceland

• Top picture is the scattering of the icebergs
  after the Jokulhlaup. (noticeable in the
  foreground is a helicopter for scale)
• Picture showing the loss of the bridge across the
  Gígjukvísl

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Case Study

• Non-Volcanic Region
• Nepal

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Nepal

• The region of Nepal in the Himalayas, in Southern
  Asia
• Due to the fast mountain building due to the
  tectonic movements has lead Nepal to have very
  steep sided mountains and valleys, in which
  glacial movement occurs

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Nepal
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Nepal

• There are 2315 Glacier Lakes in Nepal
• Despite Nepal being a 3rd world country and thus
  not contributing much to Global Warming - It is
  being affected by 0.5oC per decade rise in
  temperature
• This rise of temperature means for glaciers are
  melting and thus more hazards occurring

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Graph showing the number of Glacial Lake Outburst
Floods per year in the region
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Nepal

• The Dig Tsho failure on 4th August 1985, occurred
  due to a very warm July.
• This period of warmth caused the Langmoche
  Glacier to break and a part to plunge into the
  moraine dammed lake
• This displacement of water allowed the dam to be
  over topped and eroded the dam to allow more
  flooding to occur

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Nepal

• The Dig Tsho flood event is estimated to have
  produced 200-350m3 of flood water
• The resulting wave reached 35-50 foot high
• The whole flood event travelled 55 miles
• Although only 2 deaths were caused

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Nepal

• The flood destroyed a small hydro-electric power
  station
• Which cost 1.5 million
• The flood also destroyed 14 bridges
• Livestock and cultivated land were also lost

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References

• Björnsson Helgi, (2002), Subglacial lakes and
  jökulhlaups in Iceland, Global and Planetary
  Change, Vol. 35, Pg255271
• Richardson, S.D., Reynolds, J.M., (2000), An
  overview of glacial hazards in the Himalayas,
  Quaternary International, Vol. 65-66, Pg 31-47
• Magmilligan F.J., Gomez B., Mertes, L.A.K., Smith
  L.C., Smith N.D., Finnegan D., Garvin J.B.,
  (2002) Geomorphic effectiveness, Sandur
  development, and the pattern of landscape
  response during jökulhlaups Skeioarársandur,
  southeastern Iceland, Geomorphology, Vol. 44 Pg
  95-113
• Cenderelli D.A., Wohl E.E., (2001), Peak
  discharge estimates of glacial-lakes outburst
  floods and normal climatic floods in the Mount
  Everest region, Nepal, Geomorphology, Vol. 40, pg
  57-90

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References

• www.vulcan.wr.usgs.gov
• www.icimod.org
• www.rrcap.unep.org
• www.esri.com
• www.grida.no
• www.un.org
• www.abdn.co.uk
• www.atlas-conferences.com
• www.glaciallakemissoula.org