Oregon: Riding the Cascadia
by JD Adams

 

The legendary landscape of the Pacific Northwest beckons today much as it did centuries ago when lone mountain men returned with tales of a western world that stirred the imagination. Every year thousands of tourists flock to see wonders such as the volcanic symmetry of Crater Lake or the inexorable renewal of Mt. St. Helens. Europeans marvel at our pristine, uncrowded coastline, which they consider second to none. Oregon's charm is derived from a unique location where tectonic plates collide on the Pacific Ring of Fire, and miles beneath the surface tremendous forces are at work along the Cascadia Subduction Zone, like a slumbering giant that one day will be awakened.

There are signs that this hidden geologic power retains the potential to dramatically alter the landscape. The pressures generated by the collision of tectonic plates have resulted in lava flows in central Oregon as recently as 1500 years ago. Clear Lake was formed when lava dammed the flow of the McKenzie River. The McKenzie itself originates in the Great Spring at the north end of Clear Lake, the perpetual flow filtered through miles of porous lava deep underground. And three miles southwest of South Sister, 'the bulge' continues to puzzle scientists. First detected in 1997, the area was steadily rising upward until 2007, leading to speculation that a new volcano was forming. As of August, 2010, harmonic tremors originating there are being reported; a similar pattern of tremors preceded the Mt. St. Helens eruption. Geologists have deduced that a pool of magma about a mile across is pooling underground, although they admit they donít know exactly what is occurring. Despite many dated news reports on the Internet, the alarming growth of the bulge has subsided, yet South Sister has made National Geographic's list of the nation's ten most dangerous volcanoes. Traveling along the Cascade Lakes Scenic Byway near Bend, and hiking through the eclectic mix of wildflowers and lava flows, it's easy to forget that in terms of geologic time, this is a land in transition.

While it's likely that volcanism will continue adjacent to the Cascade Range, it is approximately 75 miles off the coast, at the meeting of the North American and Juan De Fuca plates, where energy is building with the potential for widespread events from the Cascadia Subduction Zone. Geologists studying Oregon's coast continue to find evidence that our history has been one of periodic upheaval, intermingled with and somewhat obscured by fluctuations in sea level due to climate. Volcanic eruptions, earthquakes, and landslides can generate the destructive waves known as tsunamis, which travel across the ocean at up to 500 miles an hour, and increase in height when encountering shallow water. Coastal bogs have been found buried by tsunami-driven sand, sometimes being carried inland 3 km or more. In 2008 conditions were right for unusually large amounts of sand to be removed from many of Oregon's beaches. This phenomenon revealed the gnarled remains of ancient forests that have been preserved in the sand at various places from Cape Lookout to Newport. At Neskowin, a ghost forest has become a semi-permanent attraction. Earthquakes along the Oregon coast have frequently resulted in the slumping of areas of land, burying sections of forest that have been resurrected to remind us that our coastline is a work in progress.

It is no coincidence that the term Tsunami is derived from the Japanese words for harbor and wave. On January 26, 1700, a huge tsunami bore down on the coast of Japan, originating from the Cascadia Fault Line, and causing immense destruction. Using historic information from the Japanese, field data from our coastline, and legends from Native Americans, a new understanding of the patterns of earthquakes and tsunamis has emerged. Geologists have pieced together a story that changed forever the way they perceive the relationship between earthquakes and the Cascadia Subduction Zone.

Remarkable work has been done to decipher what had formerly been regarded as poetic attempts at mythology by coastal tribes. In reality, the legends passed down by word of mouth reveal accurate accounts of earthquakes and the tsunamis that followed them. This collective knowledge allowed tribal communities to survive many such catastrophes. The legend of Thunderbird and Whale is representative of the mythology of Oregonís Tillamook Tribe, among other Pacific Northwest Native Americans. It is a classic tale of a struggle against the underworld, beginning in the ocean, coming up on land, and then subsiding after several days, each portion representing the earthquake, subsequent tsunami, and the aftershocks, respectively. Our modern society would do well to heed this ancient wisdom.

Tsunamis along the Oregon coast may be spawned from earthquakes occurring anywhere across the Pacific Ocean, and will take several hours to arrive, giving coastal inhabitants time to evacuate with the warning system that is now in place. The Cascadia Fault Line has the potential to produce earthquakes of a 9 or 10 on the Moment Magnitude Scale, which has superseded the Richter scale and is more accurate for larger events. These scales are logarithmic in nature; each increment of 1 point represents 32 times more energy released. Because of the great length of the Cascadia Fault, extending from Vancouver Island to Northern California, an earthquake on this fault could eclipse the 2004 Indian Ocean Earthquake, the third largest earthquake ever recorded with a magnitude of 9.1, which produced tsunamis 100 ft. in height. The latest research indicates that the average time between earthquakes along the Cascadia Fault Line may be only 300 years. Given that the last great quake was in the year 1700, it means that one could occur at any time. Equally significant is the proximity of the fault line Ė at a speed of 500 miles an hour, a tsunami could arrive in 15 minutes, greatly compounding the initial damage of an earthquake.

Those of the Boomer Generation may remember the Alaskan Earthquake that occurred on March 27, 1964. This megathrust, subduction zone quake went down in history as the second largest quake ever recorded with a magnitude of 9.2. Tsunamis generated by the quake killed 16 in Oregon and California. The greatest tsunami damage occurred along estuary channels where the height of the waves was amplified. At Pacific City, the tsunami brought huge amounts of debris up the Nestucca River and took out the bridge. Oregon's Cascadia Subduction Zone could produce a similar quake and tsunami, but the potential for casualties would be greater.

A recent report from the National Academies of Science concluded that even six years after the deadly Indian Ocean Tsunami, the West Coast remains unprepared for such an event. The report calls for a more uniform approach to risk assessment and warnings, and for unification of the National Oceanic and Atmospheric Administration's computer systems and software. Unfortunately, the tourism industry seeks to down-play the very real threat of tsunamis, and local residents have in some cases removed signs marking the Tsunami Evacuation routes. The only practical strategy for beach-goers is to quickly seek higher ground if shaking occurs or the ocean retreats from the shoreline, revealing the sea bed. The last sign is a roar like a train approaching. Remember, a tsunami is a series of waves, and the first wave may not be the biggest. The threat of tsunamis may persist for several hours or days, so wait for word from authorities before resuming beachcombing, wading, surfing, kite-flying, surf-fishing, romantic walks at sunset, and other idyllic activities normally done.

Copyright 2010 by J.D. Adams

Page 1