How does the erruption of a volcano effect our weather?
This is a question that a lot of people are trying to figure out. There
are two things to think about. The first is how the area very near to an
erupting volcano is having its weather affected. The second is how large
eruptions will affect the weather/climate around the world. I think more
people are worried about the second issue than the first.
As far as I know, the main effect on weather right near a volcano is that
there is often a lot of rain, lightning, and thunder during an eruption.
This is because all the ash particles that are thrown up into the
atmosphere are good at attracting collecting water droplets. We don't
quite know how the lightning is caused but it probably involves the
particles moving through the air and separating positively and negatively
charged particles.
Another problem that we are having here in Hawai'i involves the
formation of vog, or volcanic fog. The ongoing eruption is very quiet,
with lava flowing through lava tubes and then into the ocean. Up at the
vent is an almost constant plume of volcanic fume that contains a lot of
sulfur dioxide. This SO2 combines with water in the atmosphere to form
sulfuric acid droplets that get carried in the trade winds around to the
leeward side of the big Island. The air quality there has been really
poor since the eruption started in 1983 and they are getting pretty tired
of it. It also seems as if the amount of rain on that side of the island
has been low during the same time. You might think that with all those
sulfuric acid particles floating around there would be plenty for rain
drops to nucleate on but the explanation I heard was that thes droplets
are all the same size and for good rain nucleii you want a variety of sizes.
As for the world-wide affects of volcanic eruptions this only happens when
there are large explosive eruptions that throw material into the
stratosphere. If it only gets into the troposphere it gets flushed out by
rain. The effects on the climate haven't been completely figured out. It
seems to depend on the size of the particles (again mostly droplets of
sulfuric acid). If they are big then they let sunlight in but don't let
heat radiated from the Earth's surface out, and the net result is a warmer
Earth (the famous Greenhouse effect). If the particles are smaller than
about 2 microns then they block some of the incoming energy from the Sun
and the Earth cools off a little. That seems to have been the effect of
the Pinatubo eruption where about a 1/2 degree of cooling was noticed
around the world. Of course that doesn't just mean that things are
cooler, but there are all kinds of effects on the wind circulation and
where storms occur, and just about anything else you can think of. Some
folks think that large eruptions can cause the weather phenomena called
"El Nino" to start. This is a huge disruption of the Earth's atmospheric
circulation. The connection hasn't been accepted by everybody though.
An even more controversial connection involves whether or not volcanic
activity on the East Pacific Rise (a mid-ocean spreading center) can cause
warmer water at the surface of the East Pacific, and in that way generate
an El Nino. Dr. Dan Walker here at the University of Hawai'i has noticed
a strong correlation between seismic activity on the East Pacific Rise
(which he presumes indicates an eruption) and El Nino cycles over the past
~25 years. Lots of people seem not to like this idea, but it hasn't been
disproved either.
Hopefully this will give you an idea of the connections between two of the
Earth's more complex features, volcanoes and climate.
sincerely,
Scott Rowland, University of Hawaii
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