Volcanoes
that have not erupted for some time are dormant, and volcanoes that
have not erupted even in the distant past are called extinct. Volcanic
activity and volcanic eruption is usually triggered by alterations of
tectonic plates, resulting in landslides or earthquakes.
There are different types of volcanic eruptions: -
Phreatic:
explosion of steam, water, ash and rock as magma comes in contact with groundwater or surface water -
Rhyolite flow: high-silica lava (>68%) -
Basalt flow:
low-silica lava (when the silica content is low, lava usually has a higher magnesium and iron content) -
Pyroclastic flow: fast-moving hot ash, gas and rock
- Lahar: mudflow of pyroclastic material into a river valley
- Carbon dioxide emission
Volcanic eruptions can be extremely damaging to the environment,
particularly because of a number of toxic gases possibly present in
pyroclastic material. It typically consists mainly of water vapour, but
it also contains carbon dioxide and sulphur dioxide gas. Other gases
typically found in volcanic ashes are hydrogen sulphide, hydrogen
chloride, hydrogen fluoride, carbon monoxide, and volatile metal
chlorides.
Carbon dioxide emitted from volcanoes adds to the natural greenhouse effect. Sulphur dioxides cause environmental problems,
because they are converted to sulphuric acid in the stratosphere; the
main cause of acid rain. Furthermore, sulphate aerosols are formed,
which reflect solar radiation and absorb heat, thereby cooling the
earth. Sulphate aerosols also take part in chemical reactions, forming
ozone destructive material.
An example of a volcanic eruption that caused substantial environmental damage is the Mount Pinatubo eruption in the Philippines.
The eruption of the Eyjafjallajokull volcano is unlikely to have any
significant impact on climate but has caused a small fall in carbon emissions, experts say.
Although
large eruptions such as Mount Pinatubo in 1991 can spew out enough
material to shade and cool the planet, recent activity in Iceland
is very small in comparison. The ash cloud has not reached the high
atmosphere, where it would have the most effect, and it contains little
sulphur, which forms reflective droplets of sulphuric acid. The World
Meteorological Organisation in Geneva says any cooling effect from
Eyjafjallajokull will be "very insignificant".
A larger effect on the atmosphere, though still small in global terms, comes from the mass-grounding of European flights
over the past few days. According to the Environmental Transport
Association, by the end of today the flight ban will have prevented the
emission of some 2.8m tonnes of carbon dioxide since the first flights were grounded.
The
volcanic eruption has released carbon dioxide, but the amount is
dwarfed by the savings. Based on readings taken by scientists during the
first phase of Eyjafjallajokull activity last month, the website Information is Beautiful calculated the volcano has emitted about 150,000 tonnes of CO2 each day. Worldwide, the US Geological Survey says volcanoes produce about 200m tonnes of carbon dioxide every year.
•
This article was changed on 21 April. It originally said the volcano
has emitted about 15,000 tonnes of CO2 each day. Information is
Beautiful has since corrected this figure to 150,000; we have updated our article to reflect this
Lava flows are almost always too slow to
run over people, but they can certainly run over houses, roads, and
any other structures.
Pyroclastic flows are mixtures of hot
gas and ash, and they travel very quickly down the slopes of volcanoes.
They are so hot and choking that if you are caught in one it will kill
you. They are also so fast (100-200 km/hour) that you cannot out-run
them. If a volcano that is known for producing pyroclastic flows is
looking like it may erupt soon, the best thing is for you to leave
before it does.
Some of the good ways that volcanoes
affect people include producing spectacular scenery, and producing very
rich soils for farming.
Gases
Water vapor, the most common gas
released by volcanoes, causes few problems. Sulfur dioxide, carbon
dioxide and hydrogen are released in smaller amounts. Carbon monoxide,
hydrogen sulfide, and hydrogen fluoride are also released but typically
less than 1 percent by volume.Gases pose the greatest hazard close to
the vent
where concentrations are greatest. Away from the vent the gases
quickly become diluted by air. For most people even a brief visit to a
vent is not a health hazard. However, it can be dangerous for people
with respiratory problems.
The continuous eruption at Kilauea presents some new problems. Long term
exposure to volcanic fumes may aggravate existing respiratory problems.
It may also cause headaches and fatigue in regularly healthy people.
The gases also limit visibility, especially on the leeward side of the
island where they become trapped by atmospheric conditions.
A deadly eruption
The 1815 explosive eruption of Tambora volcano in Indonesia and the subsequent caldera collapse produced 9.5 cubic miles (40 cubic
kilometers) of ash. The eruption killed 10,000 people. An additional
80,000 people died from crop loss and famine.
Aircraft
To put it mildly, ash is bad for jet
aircraft engines. Apparently the problem is much more severe for modern
jet engines which burn hotter than the older ones. Parts of these
engines operate at temperatures that are high enough to melt ash that
is ingested. Essentially you end up with tiny blobs of lava inside the engine. This is then forced back into
other parts where the temperatures are lower and the stuff solidifies.
As you can imagine this is pretty bad. One problem that I heard about is
that pilots start losing power and apply the throttle, causing the
engine to be even hotter and melt more ash.Added to this is the fact
that ash is actually tiny particles of glass plus small mineral
shards–pretty abrasive stuff. You can imagine that dumping a whole bunch
of abrasive powder into a jet engine is not good for the engine. This
has been a pretty non-scientific explanation of the problem. I just
found an article that describes the problem a little more technically.
“The ash erodes sharp blades in the
compressor, reducing its efficiency. The ash melts in the combustion
chamber to form molten glass.
Safe distance
The distance you have to evacuate
depends entirely on what kind of eruption is going on. For example,
Pinatubo, one of the largest recent eruptions sent pyroclastic flows at
least 18 km down its flanks, and pumice
falls were hot and heavy even beyond that. For example, pumice 7 cm
across fell at Clark Air base which is 25 km from the volcano! A 7 cm
pumice won’t necessarily kill you but it does mean that there is a lot
of pumice falling, and if you don’t get out and continuously sweep off
your roof it may fall in and you’ll get squashed.On the other hand, the
current eruption at Ruapehu is relatively small. In fact, there were
skiers up on the slopes when the eruptions commenced, and even though
they were only 1-2 km from the vent they managed to escape. The
volcanologists routinely go up on the higher slopes of Ruapehu during
these ongoing eruptions to collect ash and take photographs.
So you see, you need to know something
about what you think the volcano is going to do before you decide how
far to run away. I guess if you have no idea of what the volcano is
planning, and have no idea of what it has done in the past, you might
want to be at least 25-30 km away, make sure you have a good escape
route to get even farther away if necessary, and by all means stay out
of low-lying areas!
Cities and Towns
The effect an eruption will have on a
nearby city could vary from none at all to catastrophic. For example,
atmospheric conditions might carry ash away from the city or topography
might direct lahars and pyroclastic flows to unpopulated areas. In
contrast, under certain atmospheric, eruption and/or topographic
conditions, lahars, pyroclastic flows, and/or ash fall could enter the
city causing death and destruction.
This scenario brings up several
interesting problems. How do you evacuate a large population if there
is little warning before the eruption? Where do these people go? If an
eruption is highly likely yet hasn’t happened yet how long can people
be kept away from their homes and businesses?
I should point out that in most volcanic
crises geologists advise local civil defense authorities. The civil
defense authorities decide what to do concerning evacuations, etc.
The IAVCEI has
a program to promote research on “Decade” Volcanoes. Decade volcanoes
are likely to erupt in the near future and are near large population
centers. Mount Rainier in Washington and Mauna Loa in Hawaii are two
Decade volcanoes in the U.S. Other Decade volcanoes include Santa Maria,
Stromboli, Pinatubo, and Unzen.
What happens to the towns around a
volcano when it erupts depends on many things. It depends of the size
and type of eruption and the size and location of the town. A few
examples might help. The 1984 eruption of Mauna Loa in Hawaii sent lava
towards Hilo but the eruption stopped before the flows reached the
town. The 1973 eruption of Heimaey in Iceland buried much of the nearby town of Heimaey under lava and cinder. The 1960 eruption of Kilauea in Hawaii buried all of the nearby town of Kapoho under lava and cinder. In 1980, ash from Mount St. Helens fell on many towns in Washington and Oregon. The 1902 eruption of Mount Pelee on
the island of Martinique destroyed the town of Saint Pierre with
pyroclastic flows. In 1985, the town of Armero was partially buried by
lahars generated on Ruiz. For more examples see Decker and Decker
(1989).