"I've got a quick question for the physicists out there."
It may be a quick question, but the answer is NOT quick! :-)
"I have been discussing the Yellowstone area on another group
working with fossil forests etc.. It seems that the whole are
is made up of volcanic materials overlying older sedimentary
rock. This implies to me that the volcanoes must have come about
at a point after the flood."
I have difficulties relating the last sentence, and what follows,
to the Yellowstone fossil forest. The Lamar River site used to
be regarded as "in-situ" growth of successive forests. But the
evidences for the "forests" being transported in mud and debris
flows is overwhelming. These rocks and the enclosed fossil flora
are linked to volcanism, but they are sedimentary and water laid.
Cooling is not an issue here.
"My question is how long does it take an active volcano to cool
to ambient temp."
A physical model needs to be developed if this question is to
have a quantitative answer. The crucial issues relate to the
relative contributions of conduction and convection. Convective
heat losses can be very high in the presence of water. If the
model permits the convective movement of water in the rocks
surrounding the hot intrusion, the heat losses can be
substantial: far greater than the conductive losses. Examples
of convective heat loss are the hydrothermal systems associated
with hot oceanic ridges. The physical model must also address
the question as to whether there is a continuing energy input to
the system being studied. "Active" volcanoes today have to be
treated differently from "inactive".
[snip]
"So taking a Grand Teton or Mt. St. Helen example how long does
it take a mass of lava at x temp to cool to the ambient temp of
the rock around it? Months, years or thousands of years? I
really don't have any feel for what the answer would be."
If conductive cooling is dominant, it may take thousands of
years, depending on the size of the intrusion. But most volcanic
systems today have some convective cooling (because they are near
the surface). The timescales then depend entirely on which
characteristics are built into the model.
Another example of hydrothermal cooling relates to hydrothermal
energy projects around the world. Many parts of Iceland, for
example, are supplied with hot water removed from below ground.
Yellowstone has its fair share of hydrothermal water - but who
would dare try to extract it!
Best wishes,
*** From David J. Tyler, CDT Department, Hollings Faculty,
Manchester Metropolitan University, UK.
Telephone: 0161-247-2636 ***