February 06, 2005

Nature: More Powerful Than Humans

A naďve and touching characteristic of human beings is to imagine that we control the world. Somehow we believe we are agents who can own, shape and exploit nature, and therefore, we are in charge. And, indeed, humans are significant forces on shaping the world we know today. Certainly we affect the natural world in fairly serious ways as witnessed by the encroaching global climate change that will shape the lives of all humans and most other living creatures in a very short time. Nevertheless, the natural world is more complex than we often imagine and it is capable of awesome acts that can astonish and frighten us. The 9.0 Earthquake and resulting tsunami in Indonesia demonstrate that there are things of this earth well beyond our puny control. Such natural disasters humble us.

Today, knowledgeable people recognize that most geological change of the earth operates at glacial pace through the steady wearing away of rock by wind and rain, yet there are times when the natural forces build up significant stresses which are then released in dramatic events. Our world is a dynamic, changing planet which sometimes seems to be a living being that exists on a timescale almost incomprehensible to humans. Indeed, human lives are insignificant when measured on a geologic scale. Yet, it is the dynamic and malleable nature of the earth that has created the only home we know even when it at times becomes a frightening and inhospitable host.

One of the more fascinating stories that science can tell us is the story of the earth. Just as earthquakes and volcanoes deform, build and change the land, ice, wind and water are forces that carve away mountains, reshape the plains and wash away and redeposit the very land. When we think about the geologic processes that are the most impressive, we often reflect on the volcanoes and the earthquakes that cause the earth to tremble. Yet as the recent tsunami showed, water can also be a force with which to reckon. Indeed, huge, catastrophic floods were significant and recurrent events in the Pacific Northwest and they shaped the land every bit as much as did the Cascades.

What caused these gigantic floods and how did they shape the landscape?

During the Ice Age that governed the earth 18,000 to 13,000 years ago, a huge ice dam was created at the head of the Missoula valley trapping water from the Clark Fork River which created the Glacial Lake Missoula. The ice dam captured an enormous amount of water, enough to fill Lake Erie and Lake Ontario combined, and the lake depth would reach 2000 feet at foot of the dam. As the lake filled, eventually the turbulence of the water undercut the dam which eventually led to a catastrophic failure of the dam.

Once the dam failed, geologists believe that the entire lake drained within 2 to 3 days. It must have been an incredible sight to see such a huge dam fail and that much water thunder out. The waters and its cargo of ice and debris carved their way from Montana, through the Idaho panhandle, down the eastern Washington plain and then used the Columbia River as its channel to the sea. And even more astonishing, these massive floods didn’t happen just once, but geologists now believe these floods occurred a number of times until the massive ice sheet retreated.

Obviously, floods on this scale would do a considerable amount to shape the landscape. Today, we see the results of those floods throughout their path to the ocean. In Eastern Washington, the barren channeled landscape and the coulees are stark evidence of the passage through this land. Also found there is a landscape feature called the Dry Falls, which at one time was the largest waterfall in the world. The water fell over a cliff face stretching 3 ˝ miles for a 400 feet drop. (As a comparison Niagara Falls drops over a cliff face extending one mile and falls 165 feet.) As the water raced through Eastern Washington, it created the landscape known as the scablands by stripping away the topsoil (in some places over 250 feet deep) and carried it downriver.


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Dry Falls in the Washington Scablands
[Photo courtesy of John Shaw]

The topsoil from Eastern Washington was carried down river along with the ice and other debris ranging from the size of the huge boulders to the silt that made up the topsoil. Today, the Willamette Valley is one of the world’s most fertile valleys, blessed with temperate weather and incredibly good soil. It turns out that Willamette Valley was the happy recipient of some of the fertile volcanic topsoil ripped off the Eastern Washington plain. When the flood waters reached Portland (with a depth approximately 400 feet more than a normal flood stage for the river), a backwater was created that flooded the Willamette Valley and extended upstream through the valley all the way to Eugene, Oregon. When the waters retreated they left Missoula flood deposits that are 100 feet thick in some places. And they also left enormous house sized boulders that had been carried downstream encased in ice. Even so, only a very small amount of the debris was left in the valley and over 99 % of the debris carried in the raging waters was lost to the sea.

If you come to Portland, the Max (lightrail) station under the west hills for the Zoo and the Forestry Center has a 270 foot long core extracted from where the elevator shaft was drilled from the surface to the Max stop inside the tunnel. This core contains the geologic history of the west hills. The evidence of a number of Bretz floods are sandwiched between lava flows showing a cycle of volcanic eruption and ice dam failures. To me, this geologic story of the Pacific Northwest is as amazing as the tale of how the Grand Canyon came to be.

We humans are along for the ride on this incredible voyage of the earth through time. When the earth twitches, the consequences for humans can be tragic as the recent earthquake and tsunami showed. Yet, there is beauty in the relentless processes of the earth. We humans could not live without the exquisite dance of our lovely (and powerful) planet with its core of molten rock, its wandering continents, the frightening volcanoes and earthquakes, and the never-ending wind and water that seek to smooth out and grind down the indomitable rocks.

[First published in Vox Populi Nebraska, January 2005]

Posted by Mary at February 6, 2005 01:48 AM | Science | Technorati links |
Comments

Oregon and Washington coastal residents really need to take a heads from the Indian Ocean nine-pointer and the resutlant tsunami, the Juan de Fuqua is primed to do the very same thing. The Juan de Fuqua plate is being subducted under the North American plate, growing smaller as the Pacific plate continues to force its movement eastward. A little over a hundred miles off the Washington coast, it has "slipped" - a subduction earthquake precisely the same as the Dec.26 nine-pointer - between every three and hundred years 'ore the past sixteen hundred years, the last in 1700. That slippage moved the coastline inland in some places up to a thousand feet.

The over-riding plate in the Dec. 26 nine-pointer rose at the point of subduction as much as three hundred feet. We were unable to see much of the earthquake damage as such as the tsunami damage was virtually immediate and washed much away. Try to imagine, though, what happens to buildings riding on such an upthrust, or even an upthrust of a few yards. Building would literally be flipped in the air, much as one would flip a cigarette butt from thumb and ring-finger. And though much of Sea-Tac is protected by the peninsula, the Puget inlet could service as an amplifier of a resultant tsunami.

Though earthquake effect may be less profound at Portland/Vancouver, coastal towns could easily be obliterated, and the tsunami itself could easily reach both San Fransisco and Eugene, which already has an active volcano pointed at her.

Out here on the High desert? Well, 'ya have to wonder about the city-fathers penchance for un-controlled growth...

Posted by: Thomas Ware at February 6, 2005 10:18 AM