Impact of rainfall reaches to roots
of mountains
University of Toronto
The erosion caused by rainfall directly affects the movement
of continental plates beneath mountain ranges, says a University
of Toronto geophysicist — the first time science has
raised the possibility that human-induced climate change could
affect the deep workings of the planet.
“In geology, we have this idea that erosion’s
going to affect merely the surface,” says Russell
Pysklywec, a professor of geology who creates computer models
where he can control how a range of natural processes can
create and modify mountains over millions of years. Pysklywec
conducts field research in the Southern Alps of New Zealand,
where the mountains are high and geologically “young.”
He found that when mountains are exposed to New Zealand-type
rainfall (which causes one centimetre of erosion per year)
compared to southern California-type rainfall (which erodes
one-tenth of a centimetre or less), it profoundly changes
the behaviour of the tectonic plates beneath the mountains.
“These are tiny, tiny changes on the surface, but
integrating them over geologic time scales affects the roots
of the mountains, as opposed to just the top of them,”
says Pysklywec. “It goes right down to the mantle
thermal engine — the thing that’s actually driving
plate tectonics. It’s fairly surprising — it hasn’t
been shown before.”
It takes a supercomputer several days to run one of Pysklywec’s
models, which reveal the inner workings of the Earth to hundreds
of kilometres below the surface, where the temperature can
reach 1,500 degrees Celsius. In extreme conditions, he says,
the erosion effect can even cause the underlying plate to
reverse direction. “As a concept, imagine blanketing
the European Alps with a huge network of ordinary garden sprinklers.
The results suggest that the subtle surface weathering caused
by the light watering have the potential to shift the tectonic
plates, although you would have to keep the water on for several
million years.” In the long run, says Pysklywec,
it raises the question of whether human activity, which is
affecting climate, could ultimately influence deep Earth processes.
“That’s what these findings suggest,”
he says. “We’re talking millions of years, but
it’s one more example of how all these natural systems
are interrelated.”
The study appears on the cover of the April issue of Geology
and was funded by the Natural Sciences and Engineering Research
Council of Canada and Lithoprobe.
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