A
supervolcano refers to a volcano that
produces the largest and most voluminous kinds of eruptions on earth.
The actual explosivity of these eruptions varies, but the sheer volume
of extruded magma is immense enough to radically alter the landscape
and severely impact global climate for years, with a cataclysmic
effect on life. The term
was originally coined by the producers of a BBC Popular Science
programme in 2002 to refer to these types of eruptions. Though there is
no well-defined minimum size for a "supervolcano", there are at least
two types of volcanic eruption that have been identified as
supervolcanoes.
Since
there is no firm definition of what a
super volcano is, it's hard to say how many of them are found on the
earth. Usually people list Long Valley in eastern California and Taupo
in New Zealand as super volcano sites along with Yellowstone National
Park. The last
known explosion of what might be considered a super volcano was Toba in
Indonesia. Toba erupted with a huge explosion about 74,000 years ago.
The force of the explosion was estimated to be 10,000 more powerful
than the blast that destroyed Mount St. Helens, in Washington.
Tremendous
amounts of rock and ash were ejected into the air, blocking
the sun for months. The temperature around the globe was thought to
have plummeted as much as 21 degrees. Man was pushed to the edge of
extinction, the population forced down to just a couple of thousand.
Perhaps as much as 75% of plant life on the North American continent
may have died out.
What causes a Super Volcano
A
super volcano differs from a regular
volcano in that there is often no mountain peak associated with it. In
a regular volcano hot magma under pressure flows up from the depths of
the earth. A hole forms in the surface and the magma, now lava, pours
out. As it cools, it forms a cone that eventually builds up into a
mountain. If the passage is blocked off, the pressure can build up in
the mountaintop and explode with a monstrous force. That's what
happened at Mount St. Helens. The pit formed by the explosion becomes
the new caldera.
In a super
volcano the magma is blocked from
ever reaching the surface. Instead, the pressure just builds and builds
until more and more rock in the area melts and becomes magma too. The
area under the surface becomes one huge underground sea of semi-molton
rock.
Finally, the
pressure becomes too much to hold back and the entire
surface above the underground chamber, which can be many miles wide, is
blown away by a huge explosion that can be thousands of times more
powerful than that of a regular volcano.
Super volcanoes
are found throughout the world, there is even evidence
to prove that there is a super volcano beneath Loch Ness, Scotland.
Loch Ness lies on the Great Glen fault-line and its incredible depth
(over 2km) has severely hampered researchers progress. Fortunately new
developments with satellite laser topography sonar side-scanning
techniques have enabled us to penetrate through the thick sludge that
lies up to 400m thick at the loch's bottom.
The latest
eruption of Mt. Etna in Sicily, which had destroyed a few
buildings, shut down the airport and crept into a ski area, produces
dramatic nighttime video of hot rolling lava and explosive fireworks.
But compared to the known history of volcanoes and even its own past,
Etna's 2001 pyrotechnic show is so far geologically pathetic.
Likewise, the
eruption of Mt. St. Helens in 1980 was a volcanic sneeze
compared to what scientists say America will experience one day. And a
mysterious four-inch-high bulge in the ground of central Oregon is, so
far, little more than a conversation piece.
Sooner or later,
geologists warn, a "super volcano" will strike. Some
scientists in this field will even go so far as to say that phenomena
like this one pose a greater threat than terrorism.
When will one next erupt?
Scientist
have discovered that the
ground in Yellowstone is over 70cm higher than in was in 1923 -
indicating a massive swelling underneath the park. The reservoir is
filling with magma at a staggering rate. The volcano erupts with a
calendar-like cycle of every 600,000-650,000 years. The last eruption
was more than 640,000 years ago - we could be running late.
What would be the effect of an eruption?
Let's
use Yellowstone. Immediately
before the eruption, there would be large
earthquakes in the region.
The ground would swell further with most of the area being uplifted.
One earthquake
would finally break the
layer of rock that holds the
magma in - and all the pressure the Earth can build up in 640,000 years
would be unleashed in a cataclysmic
event.
Magma
would be flung more than 50
kilometres into the atmosphere. Within a thousand kilometres virtually
all life would be killed by falling ash, lava flows and the sheer
explosive force of the eruption. Volcanic ash would cover places
thousands of miles away. One thousand cubic kilometres of lava would
pour out of the volcano itself, enough to coat the whole of the USA
with a layer a few inches thick. The explosion would have a force
1000-2500 times that of Mount St. Helens. It would be the loudest noise
heard by man for more than 75,000 years, the time of the last super
volcano eruption. Within minutes of the eruption tens of thousands
could be dead.
The long-term
effects would be even more devastating. The thousands of
cubic kilometres of ash that would shoot into the atmosphere could
block out light from the sun, making global temperatures fall
dramatically. This is called a nuclear winter. As during the Sumatra
eruption a large percentage of the world's plant life would be killed
by the ash and severe drop in temperature. Effects world wide would
cause massive food shortages. If the temperatures decline by the 21
degrees they did after the Sumatra eruption the Yellowstone super
volcano eruption could truly be an extinction
level event.
Humans could be
pushed to the edge of extinction.
Anthropologists
suggest it won't be the first time.
But well before
such a calamity, warning flags will likely show up on
the computers of geologists around the world who monitor an
increasingly useful stream of satellite data. There have also been more
pushes by scientists in the field to 'wake up' and devote more
attention to this, it's truly startling.
