On 3 May 2001 the Caltech Alumni Association sponsored a field trip to Great Falls National Park on the Potomac River upstream from Washington, DC. Retired geologist E-an Zen gave a brisk walking commentary:
|Those logs? The flood of 1996|
Left them as driftwood way up on that cliff.
The valley was submerged. Just think,
When 30 inches of snow melted, all
Within a day or two, the runoff had
To make it through this gorge. The crest
Rose 70 feet or more and moved
Those meter-sized boulders. Amazing, yes?
And potholes! Let me show you how the stream
Made vortices against the side of this
Formation. Alcoves here were cut so fast ---
An inch a year --- that you could almost watch
Them form if you were patient. Fingernails
Grow just as rapidly. A big pothole
Develops in a human life. That's quick!
If you come back here in 10,000 years
You'll see something quite different. The land
Is lowering about a millimeter
Every century. This boulder that
We're standing on came down the river in
A flood about a quarter million years
Ago; it moved some fifty miles. And see
The patch of lichen here? It grows so slow
That by its size you know it's centuries
Old now. So we can tell this rock has not
Been much disturbed; beryllium that's formed
By cosmic rays which hit the surfaces
Provide us with a measure of its age.
And note this mica schist: it must have been
Pressed under 10 kilometers at most
Of overburden, 900 Centigrade,
To partly melt the crystals. That suggests
A geothermal gradient far more
Than anything that's normal nowadays
In Appalachian land. We're looking at
A half a billion years of history.
Kinda puts today's problems into a slightly larger perspective. (Many thanks also to Alumni Association Deputy Director Arlana Silver and to Dr. Dallas Peck, for organizing and running the expedition.)
Wednesday, May 09, 2001 at 05:47:38 (EDT) = Datetag20010509
TopicPoetry - TopicProfiles - TopicScience - TopicPersonalHistory
(correlates: BigLessons, UnclosetedSkeletons, SimplifyingThroughComplexity, ...)