Monday, July 16, 2007
Earth Science for the Layman
Son Keith Views NW Beauty after the heat in IRAQ
EARTH MOVEMENTS ON WHIDBEY ISLAND
When I arrived on this island in the Puget Sound, 10 years ago, the few workers I could find in Earth Science said “There’s nothing of interest on this 14,000 year old piece of land- just Dirt Geology” So I resolved to remain taciturn and find out for myself about Nature’s Truths.
It is true that most of W.I. is covered by Glacial Till from the last ice age. This unsorted sediment which formed underneath as much as 3000 feet of ice (dropping from entrainment in the ice, due to melting of the overlying glacier) makes poor soil, since it had very little organic material in it. But there were several inter-glacial periods between south or westward movements of the ice, and I resolved to find mastodon bones in the accompanying bogs and wetlands. I found few fossils, but the beach walks yielded much more than bones.
I did find a few thin clam shell layers in the beach cliffs, but mostly there were indications of destruction of the several somewhat compacted sedimentary formations which have remained. In the photos and descriptions to follow, I hope to show you that the island is a treasure trove of Pleistocene events- cliff walls containing simple stratigraphy with occasional massive disruptions. These show a record of earth movements in the last ¼ million years. The waxing and waning of glaciers goes back almost two million years, but only the last three cycles are seen in Whidbey cliffs. In order of increasing age, these are named Frazer, Possession, and Double Bluff, where the first is a Canadian River, the second occurs most prominently at the Possession Point, south, end of the island, and the oldest occurs at Double Bluff cliffs, near Freeland. The older glacial periods of warming show that there were many peat beds (from trapped vegetation), earthquake-formed distortions- called cauliflower structures (after the shape), and slicing of the older sedimentary layers (factures and faulting).
It was already well documented that metasediments occurred near the Deception Pass bridge (Whidbey is a true island, but within a mile of other islands connecting to the mainland in Skagit County).One may drive to the north end of the island, to the DP bridge, eliminating the need to access the auto ferry on the south end- at Clinton. The metamorphic (change of form due to pressure and temperature at depth) rocks are true stone at the north end, not like the pre-stone of 95% of the W.I. surface. These metasediments are of Cretaceous age or older (100 million years or so) and are very hard.
Normally geologists describe rocks or stone of many million years antiquity, so that the rock is hard, resistant to erosion, and difficult to break or cut with a knife. On W.I. the oldest of the till and sand has not been cemented or compressed sufficiently to yield more than compacted sand. This Pre-stone makes fair cliffs, some almost vertical, but it has insufficient strength to survive winter storms, and can usually be scratched with the fingernail.
The Earth movements, although subtle, can be traced cross-country by use of saddles in the topography, and more starkly, in the cliffs. When one of the USGS researchers remarked to me “You cannot find a fault on the ground surface of Whidbey island that you may walk on”, I was able to reply that you can indeed walk on two of them at low tide, between Baby Island and Saratoga Road on the larger island.
Most of the island is covered with vegetation, so that one can only view the stratigraphy in the cliffs at the beaches, but there are a few other clues:
a. The main glaciation oriented north to south, as it advanced. This creates drainageways or grooves in the surface which one can see in the interior. Other orientations yield information about subsequent events, other than glaciation;
b. Bays or indentations in the island are likely created by faulting which presented an opportunity for increased erosion;
c. Sinkholes are the result of ice being isolated as large chunks, leaving Kettles whenever the ice later melted. Interior drainage wetlands probably derive from a similar situation;
d. Dune sand occasionally occurs in the interior, resulting from wind having deposited river-brought sand away from the beach;
e. Present creeks orienting at some angle other than N-S, indicate subsequent earth movement; and,
f. Concrete breakage and road repair indicate recent movement- probably due to active faulting.
When one hikes the beaches regularly, you can see the yearly changes as well as the pre-historical events in the cliff walls. This makes for a stimulating circumstance for your daily exercise, and one where you can get a “feeling” of the earth’s regular movement. You can determine your own assessment of what is happening with the Crust, so that it is unnecessary to resort to reading the voluminous literature opined by professional geologists. After all, they are wrong more than half the time, so form your own ideas, and keep your brain active. I have posted a link entitled Mantle plumes, which may be accessed further down the Blog (off to the right side). These show how geologist-researchers have classified, worked and re-worked, used tremendous budgets, and spent many years to obtain no conclusions. If they cannot reach a conclusion with all of the research money available, on a topic as important as the derivation of the Hawaiian chain, something must be wrong with their training! A layman can improve on this outcome, since he is not biased in advance, and is not overloaded with an outdated classification system which discourages analysis.