[meteorite-list] Volcano... Or Giant Impact?

From: Sterling K. Webb <sterling_k_webb_at_meteoritecentral.com>
Date: Wed, 19 Oct 2011 12:05:54 -0500
Message-ID: <1F47CE9F45CA4AAC8A0BE4BF76E33D8D_at_ATARIENGINE2>

An interesting study, with implications
for how we think giant impacts behave.

Sterling K. Webb

Ancient Meteorite Blast
Resembled Volcanic Eruption

A billion years ago, a meteorite slammed
into the Earth along the coast of what is
now Scotland. A forensic investigation
by a team of volcanologists has pieced
together exactly how the debris from the
impact devastated the surrounding region.
The new research shows that some
aspects of giant meteorite impacts may
mimic the behavior of large volcanic

Meteorite impacts are more common than
most people realize, but what happens when
the meteorite hits? Direct observation is
understandably difficult, but researchers
can pick through impact debris that hasn't
eroded away and then forensically
reconstruct these catastrophic events.

The volcanologists say that an improved
understanding of what happens when large
objects hit the Earth will help us understand
how such events affect life on the planet.

Volcanologists analyzed a layer of ejected
debris from this huge meteorite impact and
discovered that much of the debris moved
across the ground as rapid, dense,
ground-hugging currents of gas and debris,
remarkably similar to the pyroclastic density
currents ? fast-traveling streams of hot
ash and rock ? that flow outward from
explosive volcanoes.

"In particular, the way that ash and dust
stick together seems identical," said study
team member Mike Branney of the
University of Leicester in England.
"Moist ash from explosive volcanoes
sticks together in the atmosphere to
fall out as millimeter-sized pellets.
Where these drop back into a hot
pyroclastic density current, they grow
into larger layered structures, known
as accretionary lapilli."

The researchers studied the finely
preserved deposit in northwest Scotland
from the ancient impact. It shows both
types of these 'volcanic' particles ? pellets
and lapilli ? are produced.

"This reveals that that the 10 meter-thick
[33 feet] layer, which has been traced for
over 50 km [31 miles] along the Scottish
coast, was almost entirely emplaced as
a devastating density current that sped
outwards from the point of impact ? just
like a density current from a volcano.
Only the uppermost few centimeters
actually fell out through the atmosphere,"
said study team member Richard Brown
of the University of Durham.
Received on Wed 19 Oct 2011 01:05:54 PM PDT

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