Iceland’s recent ‘mega-flood’
An illustration of the power of Noah's Flood
by Andrew Snelling
Icelanders will long remember November 5, 1996. On that day the largest flood in
living memory swept from the terminus (bottom end) of Skeidarár Glacier.
Icelanders call such sudden drainage events jökulhlaups, literally,
‘glacier bursts.’ It is these that lead to mega-scale flooding with
devastating consequences.1
Sitting astride the mid-ocean ridge in the North Atlantic Ocean, Iceland is volcanically
one of the most dynamic parts of the Earth’s surface. Fresh eruptions occur
on average every five years. Yet, because of its high latitude, some 11% of Iceland
is covered by glacial ice.2 Indeed,
the largest currently glaciated area is called Vatnajökull, meaning ‘water
glacier,’ so common is major flooding around its margins.
The mega-flood cycle
The western half of Vatnajökull covers part of a volcanic belt (see picture),
the heat from which maintains a melted lake, even beneath the glacial ice. Known
as Lake Grímsvötn, the subglacial water is stored within a large, bowl-shaped
volcanic depression formed by the continual heat flow and periodic eruptions.3
As surrounding ice melts, Lake Grímsvötn gradually enlarges over a few
years. Ultimately it melts through an ice dam at a low point in the confining landform
and drains into a subglacial tunnel. The water usually flows southwards beneath
the 8.6-km (5.4 mile)-wide Skeidarár Glacier, discharging at its margin
some 50 km (30 miles) away as a mega-flood3 (Figure
2). The cycle starts again as the lake begins to refill.
The Vatnajökull ice-cap covers the Bárdarbunga and Grímsvötn
volcanoes. Streams radiate from the glacier’s margin, draining normal meltwater.
The Skeidarár Glacier flows south. The newly completed highway rings Iceland.
The 1996 fissure eruption filled Lake Grímsvötn, which discharged by
the subglacial flood route shown. The area flooded by the November 1996 jökulhlaup
(glacier burst) is indicated.
The 1996 volcanic eruption
At the end of 1995, fresh volcanic action beneath Bárdarbunga volcano accelerated
Lake Grímsvötn’s normal cycle. Magma at over 1100°C moved
sideways. It eventually erupted between Bárdarbunga and Lake Grímsvötn
on September 30, 1996. A 6-km (4 mile)-long fissure opened through the 450-metre
(1500 feet)-thick glacier. In just 13 days, the hot lava melted some 3 cubic km
(0.73 cubic miles) of ice.4
As the ice melted, the water drained rapidly along a narrow channel under the glacier
into Lake Grímsvötn . Apprehension grew as the subglacial lake swelled
some 60 meters (200 feet) higher than its usual trigger level.5 Over four cubic km (one cubic mile) of water had
accumulated.1 It was inevitable that the lake would
overflow and release the water, instigating a mega-flood. But when? Weeks passed
as scientists and journalists watched and waited.
The November 1996 jökulhlaup
Late on November 4, a steady ground vibration signaled that the glacier on the south-eastern
edge of Lake Grímsvötn had moved. Lake drawdown had started.3
Beneath the Skediarár Glacier the water crept at less than walking pace down
the 50-km (30 miles)-long tunnel. However, once it emerged from the end of the glacier,
about 8 AM next day, the water swept down the alluvial plain in a flood wave. In
less than two days, a volume of 3.6 cubic km (0.9 cubic miles) discharged from the
glacier, laden with sediment and transporting huge blocks of broken ice.1
The November 1996 jökulhlaup was truly catastrophic compared with the usual
mega-floods observed in the last 60 years. A normal mega-flood can take 12 days
to peak and last for 17 days, whereas this gigantic jökulhlaup peaked in 20
hours and lasted just two days. The peak discharge thus reached 55,000 cubic meters
(two million cubic feet) per second, more than five times the normal mega-flood
rate. It was the largest ever recorded in Iceland. It was over twenty times the
flow rate of Niagara Falls. In fact, the peak discharge rivaled the flow of the
Congo River, the second largest river in the world.2,5
Floodwater surged from the ice margin as new outlets developed. Blocks of ice were
ripped out, cutting huge chasms into the end of the glacier. Obstructed by inadequate
flow channels behind a major ridge of glacial rubble (terminal moraine) which largely
blocked the flow like a wall, water levels leapt higher, overflowing along new paths.
Within a few hours an enormous gorge was excavated through this ridge, at least
doubling its previous size. Downstream, a huge new channel system over 3 km (2 miles)
wide was cut into the alluvial plain.1
The consequences
During this flood, huge volumes of ice-blocks were detached from the glacier and
swept along in the raging waters. Depending on their size, some ice-blocks floated,
others rotated, bounced, skipped and slid down-channel. The biggest were 10–15
meters (33–50 feet) high and estimated to be up to 1,000 tonnes in weight.
Many huge 200-tonne blocks were strewn across the alluvial plain. Sediment up to
9 meters (30 feet) thick was deposited over an area of 500 square km (200 square
miles)—all in less than two days.6,7
Collisions by moving ice-blocks caused considerable damage. A 10-km (6-mile) segment
of the premier highway that rings Iceland disappeared (see picture). The reinforced-concrete
bridge over the Gígja River was totally swept away. The 900 meter (3000
feet) Skeidará River Bridge was severely damaged, even though its foundations
were buried to a depth of 15 meters (50 feet) to withstand mega-floods. Iceland’s
main high-tension power-lines were severed, and the telephone cables ripped apart.6,7
Relevance
Icelandic history records about 60 such cataclysms since the Vikings arrived in
the ninth century. However, scientists were skeptical of the previous awesome descriptions
of fantastic floods. Now that this mega-flood has been observed, many times larger
than previously measured, it is considered that these stories are probably true.2
At 55,000 cubic meters (two million cubic feet) per second, Iceland’s deluge
was of apocalyptic proportions. It destroyed reinforced-concrete bridges, swept
along 1000-tonne blocks of ice, eroded 3-km-wide canyons and dumped 9 meters of
sediment over 500 square km. Mercifully, it lasted only two days. Yet, on a world
scale this was only a local flood. It affected only a small part of one tiny island
on our planet. What would the global, year-long biblical Flood have achieved? Iceland’s
devastating November 1996 jökulhlaup testifies to the power of Noah’s
Flood and that it can easily explain the building of the geological record.
Skeptics who deny the historicity of the Genesis account need to learn from Iceland’s
latest mega-flood. Just because past eyewitnesses describe processes larger than
we have observed does not mean they were exaggerating.8
We need to recognize the limitations of our experience. We have not observed all
the geological processes that actually fashioned this planet.
References
- P. Worsley, ‘The 1996 volcanically induced glacial mega-flood
in Iceland—cause and consequence,’ Geology Today 13(6):222–227,
1997. Return to text.
- G. Oeland, ‘Iceland’s trial by fire,’ National
Geographic191(5):58–71, 1997. Return to text.
- P. Einarsson, B. Brandsdóttir, M.T. Gudmundsson, H. Björnsson,
K. Grönvold and F. Sigmundsson, ‘Center of the Iceland hotspot experiences
volcanic unrest,’ Eos, Transactions, American Geophysical Union
78(35):369, 374–375, 1997. Return to text.
- M.T. Gudmundsson, F. Sigmundsson and H. Björnsson, ‘Ice-volcano
interaction of the 1996 Gjálp subglacial eruption, Vatnajökull, Iceland,’
Nature 389:954–957, 1997. Return to text.
- P. Worsley, ‘Iceland: contrasting Skeidará mega-flood
hydrographs,’ Geology Today 14(3):97–98, 1998.
Return to text.
- ‘Catastrophic glacier outburst flood in Iceland,’ <http://lena.sscnet.ucla.edu/iceland.html>,
29 April, 1999. Return to text.
- M.M. Halldorsson, Jökulhlaup Update, <http://www.geophys.washington.edu/People/Students/throstho/bardb96/
flod.html>, 29 April, 1999. Return to text.
- Cf.
Genesis 6:11–8:18. Return to text.
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