Reykjavík Grapevine - 03.06.2011, Blaðsíða 21

Saturday, May 21
Grímsvötn confirmed erupting at
19:00. Ash plume reaches 15 kilo-
metres in height. It can be seen from
Reykjavík.
Sunday, May 22
Road 1 is closed between Vík and
Freysnes. Ash falls so thick in some ar-
eas that the sun is completely blocked
out until 14:00. This is described as
“öskumyrkur” or “ash darkness”.
Flights are disrupted in Iceland.
Monday, May 23
Road 1 remains closed. Wind picks up
and produces what is called a “öskub-
ylur” or “ash blizzard” near the town
Kirkjubæjarklaustur. US President
Obama leaves Ireland a day early to
avoid being grounded by the ash.
KLM and British Airways cancel hun-
dreds of flights.
Tuesday, May 24
The eruption is de facto over in the
evening and Road 1 is reopened. Ice-
landic Prime Minister Jóhanna Sig-
urðardóttir releases statement: “Our
geoscientists say that the eruption
is waning day by day and that the
problems arising in our neighbouring
countries as a result of volcanic ash
should be resolved quickly”. Hundreds
of flights remain grounded in British
airspace. Ash is expected to reach
Germany late Tuesday evening, early
Wednesday morning. Ryanair's CEO
Michael O'Leary sends test flights into
the “high ash concentration zone” and
concludes that it is “perfectly safe”
and that “there is nothing up there.”
He accuses Civil Aviation Authority of
incompetence.
Wednesday, May 25

Rain falls in the southeast and the
cleanup effort begins. President
Ólafur Ragnar Grímsson visits ash-
affected residents and farmers. Bre-
men, Hamburg, Berlin, and Hannover
briefly close their airports on Wednes-
day morning. Flights resume to normal
later that day.
lems for air traffic (something fresh in
our minds after last year). They usually
form steeper-sided peaks, similar to the
typical conical volcano image you may
have in your head.
At the top of this simplified scale
come the ‘rhyolite’ volcanoes, which
have very thick lavas that are very re-
sistant to flowing. A typical rhyolite
volcano (if there is such a thing!) could
perhaps be something like Chaiten in
Chile. They tend to erupt lavas in the
form of domes (which also occur at
andesite volcanoes), rather than spec-
tacular explosions. However, these
domes are often unstable and may then
collapse, producing the fearsome ‘py-
roclastic flow’—an avalanche of rock,
debris and hot gases. Rhyolite volca-
noes often feature enormous craters,
or ‘calderas’. Explosions may result in
some cases from rhyolitic activity, al-
though they are not common. However,
some of the largest eruptions in history
have been of this type—think of the in-
famous Yellowstone, USA…
SO HOW DOES THIS APPLY TO
ICELAND?
As I hinted at earlier, Iceland has a bit of
almost everything crammed all into one
place! Let’s look at last year’s Eyjafjalla-
jökull eruption as an example, shall we?
The first stage of the eruption,
which breached the narrow strip of
exposed land between Eyjafjallajökull
and Mýrdalsjökull glaciers, was a small
(but rather photogenic!) fissure erup-
tion. It was somewhat similar to the sort
of eruption you might see in Hawaii—
a long crack in the ground, producing
towering fountains of glowing basalt
lava and sending rivers of molten rock
pouring down the mountainside. These
lava flows even had lava falls, showing
how easily they could flow. A spec-
tacular ‘tourist eruption’, the first stage
didn’t really provide much of a threat to
anyone.
About a month later, however,
things changed. No sooner had the
fissures calmed down, but a new one
opened—this time on the summit of
the volcano, directly beneath the gla-
cier ice. This time the lava was much
different (andesite—explaining why
this happened requires an article of its
own) and this produced a much more
explosive eruption. This high explosiv-
ity, aided by the lava coming in contact
with cold melting ice from the glacier,
produced the now-infamous ash cloud
that shut down air space across main-
land Europe. While ash this fine and
troublesome is possibly quite unusual
for an Icelandic eruption, explosive ac-
tivity is really rather common.
In fact, glaciers play a major role in
Icelandic volcanism. In past times, when
the entire country was buried under
ice, the weight of the ice was enough
to constrain many eruptions and pre-
vent them from breaking through it.
Most of the long ridges and flat-topped
hills (‘tuya’) you may see as you drive
around the country are the result of
volcanism constrained by ice. Addition-
ally, as mentioned previously, the water
produced as it melts can cause explo-
sions—something responsible for even
lavas that are traditionally less explo-
sive producing quite violent eruptions.
Take the latest activity at Grímsvötn—a
basaltic eruption, if it had taken place
under plain air it would probably have
been quite benign. But because of frag-
mentation due to all that ice and wa-
ter… well, you’ve probably already seen
the result!
“But what about the rhyolite volca-
noes”, I hear one or two of you ask?
Well, if you visit one of the huge calde-
ras like Askja you are standing inside
what is known as a ‘caldera’, which are
often formed at least partly as a result
of very large rhyolite explosions. And if
you are lucky enough to visit the Land-
mannalaugar area, those fantastic yel-
low and orange colours are caused by
exposed rhyolite rocks. In fact there are
even exposed rhyolitic lava flows and
domes in this area if you look for them.
And you know what the most con-
fusing thing is? Most volcanoes in Ice-
land are in fact ‘volcanic systems’, with
a pronounced ‘central volcano’ with
a long ‘swarm’ of fissures branching
off from it. This is the result of differ-
ent types of volcanism within the same
system—often more explosive at the
central volcano and more gently ef-
fusive along the fissures. Despite this,
the source of the lavas for each erup-
tion in each system is more or less the
same. Such diverse volcanism even
within a few square kilometres poses
something of a dilemma for scientists
eager to understand what is going on
and makes Icelandic eruptions argu-
ably even harder to forecast than most!
WHAT’S NExT FOR ICELAND?
It is clear that Icelandic volcanism is
tremendously varied. It’s impossible
to tackle in any detail in such a short
space (believe me, I could go on for
days, but I suspect there wouldn’t be
anyone left reading by the end), but I
hope I have at least managed to touch
on some things that may pique your in-
terest.
In terms of what exactly Iceland
can expect in the future, no-one re-
ally knows. Volcanoes cannot be well
predicted, only roughly forecasted.
To this end, however, we can say that
in the long term it will most likely be
‘more of the same’. Iceland is a growing
country and it will continue to be volca-
nically active for a long time to come.
There will be some large eruptions and
plenty of smaller ones too. Some will
produce beautiful, glowing fountains
and some… well, Europe would be well
advised to have contingencies in place
in case of another Eyjafjallajökull!
Desert Island Destruction
My Top 5 volcanic eruptions
anywhere, ever
By James Ashworth
Listing one’s top five eruptions, anywhere,
ever, is hard work. I mean, just how do you
rate an eruption, anyway? By duration, or
the number of deaths, or just the sheer scale
of it? I really don’t know. So, I’ve just picked
five eruptions that are always memorable to
me—important for one reason or another. I
hope that’ll do! So, in no particular order…
Mt. St. Helens, USA, 1980
Starting it off with a famous one—how
very cliché. This one has a place in my list
because it was one of the eruptions that
captured my imagination early on and is at
least partially responsible for my interest in
volcanoes. It ‘only’ killed 57 people, which
was frankly a miracle, but the images of
that volcano exploding sideways are iconic
within the field. It was also very important
in our understanding of how volcanoes can
collapse, triggering a lot of very important
research, much of which is still extremely
valuable. Lessons were learnt from this one
that will be taught for years to come.
Pinatubo, Philippines, 1991
Another modern one and also rather fa-
mous. The second largest eruption of the
20th century erupted ash up to 34 kilome-
tres into the air, reducing the mountain’s
height by almost 300 metres. The ash and
aerosol particles released from Pinatubo
circled the world, resulting in an average
global temperature drop of 0.4°C. Good
evacuation plans and monitoring by a team
of Philippine and American volcanologists
undoubtedly saved thousands of lives, al-
though more than 800 people were still
killed, largely as a result of roofs collapsing
under the weight of ash and rain water. The
images of the massive ash column from this
eruption never fail to stagger me and serve
as a stark reminder of the power of nature.
Laki, Iceland, 1783-84
Now for an Icelandic one. The Laki fissures,
thought to be part of the Grímsvötn volcanic
system, erupted for eight months between
1873 and 1874. Much of the lava erupted
in massive fire fountains, reported to be
up to 1.4 km in height and spewing out a
total of 14 cubic kilometres of lava in total.
The lava itself did relatively little damage,
but the gases emitted killed much of Ice-
land’s livestock. This resulted in the deaths
of about a quarter of the Icelandic popula-
tion. Worldwide it is estimated that around
6 million people may have died due to the
Laki eruption—many of them due to short-
term climatic change triggered by the erup-
tion, which brought about famine, drought
and crop failures. Despite happening a long
time ago, there is nothing to say that this
will not happen again—rather sobering.
Unzen, Japan, 1991
Pinatubo may have stolen all of the limelight
in 1991, but another eruption in the same
year is just as big a deal for me. Unzen, lo-
cated in southern Japan, had in 1792 pro-
duced a large pyroclastic flow that triggered
a megatsunami, which claimed the lives of
an estimated 15.000 people. The 1991 erup-
tion was much more modest (although not
small!), but again produced a pyroclastic
flow. This time 43 people were caught in
its path, including legendary French vol-
canologists and filmmakers Maurice and
Katia Krafft. Especially poignant since I
have visited this volcano, it serves to remind
me that no matter how well you think you
understand something, it can always come
back to bite you.
Yellowstone Caldera, USA,
640.000 years ago
What list would be complete without good
old Yellowstone? If ever you don’t find vol-
canoes terrifying enough, you can always
look here. Eruptions like Pinatubo and Laki
seem enormous, but they pale in compari-
son with Yellowstone, which has produced
several massive explosive ‘super-eruptions’
during its lifetime. During the last such
event, the caldera ejected about 1.000 cu-
bic kilometres of rock—compare that to
Laki! The Yellowstone caldera (crater) is
about 55 by 72km in size, which is frankly
hard to comprehend. Its history of destruc-
tion is offset rather by the immense beauty
and rich ecosystems now contained within
the caldera. Having visited Yellowstone
three times, it is safely one of my favourite
places... but at the back of your mind you al-
ways know that at some point it will almost
certainly happen again...