Title: Jkulhlaups:
1Jökulhlaups
Hemis Number 161760 2GS333 Geohazard Management
and Remediation
2What is a Jökulhlaup
- Jökulhlaup is icelandic for Glacier Floods
- Otherwise they are known around the world as
Glacial Lake Hazards - Or Glacial Outburst Floods
3Where 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
4Examples of Locations
- The Cascades USA
- Wisconsin USA
- Grimsvötn Iceland
- Himalayas Nepal, Bhutan
- Andes - Peru
5How 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
6How 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
7Subglacial 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
8How 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
9How 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
10Effects
- 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
11Effects
- 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
12Geomorphology 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
13A map of the North American scablands
14Geomorphology Changes - Evidence
Top left shows Ripple Marks Top Right shows
erratic blokes Bottom Left Shows Debris (with the
front left bloke being 5foot high
15Monitoring
- 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
16Monitoring
- 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
17Monitoring
- 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
18Remediation 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
19Mitigation
- 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
20CASE STUDY
21GrÃmsvötn 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 GrÃmsvötn being the largest subglacial lake
in Iceland.
22GrÃmsvötn 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
23GrÃmsvötn Iceland
- GrÃmsvötn 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
24GrÃmsvötn Iceland
G
Map of Iceland showing the volcanoes and ice caps
25GrÃmsvötn Iceland
Map of the Vatnajökull glacier, showing GrÃmsvötn
volcano
26GrÃmsvötn Iceland
- GrÃmsvötn 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
27GrÃmsvötn 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
28GrÃmsvötn Iceland
- Time Scale
- 4th November 1996 2130
- High frequency constant tremors recorded at
GrÃmsfjall 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.
29GrÃmsvötn 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
30GrÃmsvötn Iceland
- Time Scale
- 5th November 1996 1pm
- The bridge across the glacier river GÃgjukvÃsl
had been destroyed in the flood - Power lines and telephone lines cut
- 5th November 1996 6pm
- The Bridge across SæluhúsakvÃsl destroyed
- Flow rate estimated at 25000m3/sec
- 10million worth bridge spanning Skeiðará is
severely damaged
31GrÃmsvötn Iceland
- Time Scale
- 6th November 1996 9am
- The Jökulhlaup reached speeds of 45000m3/sec
- Bridges across SæluhúsakvÃsl and GÃgjukvÃsl
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
32GrÃmsvötn Iceland
- Despite the size of the flood caused by the
volcanic activity there was only 0.4Km3 of
volcanic material emitted
33GrÃmsvötn 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
GÃgjukvÃsl
34Case Study
- Non-Volcanic Region
- Nepal
35Nepal
- 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
36Nepal
37Nepal
- 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
38Graph showing the number of Glacial Lake Outburst
Floods per year in the region
39Nepal
- 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
40Nepal
- 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
41Nepal
- 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
42References
- 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
43References
- 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