"The Cascadia Earthquake and the Bonneville Landslide" by Tom Dunn
To encourage our readers, Creation Encounter leaders have been writing a series of essays reminiscing on the adventures and blessings of last year as we look forward to encountering our Creator with you this summer. Creation Encounter guide Tom Dunn continues this series with an essay on the connection between the Cascadia Earthquake of AD 1700 and the Bonneville Landslide. Please enjoy and feel free to share your own stories with us!
By Tom Dunn
A new hike that I have been helping Steve Hayley on is the West Gorge Trip. Two things that really fascinated me were the Cascadia Earthquake and the Boring Volcanoes. I was so interested in the Cascadia Earthquake/Bonneville Landslide that I asked Steve if I could give the talk on it the next time we did the hike together. Well, I thought I had better do some of my own research before I gave the talk, and I’m glad I did.
We take our group to Thunder Island in Cascade Locks. We then take them about 100 yards to the far side of the island and have them look across the Columbia due north and ask them what they see. Someone usually notices that a big section of Table Mt. is missing. Yes, that is correct. We then point out that this section of the Columbia was known for its rapids and large rocks in the water. Then we take them to Lewis and Clark’s journals where it point out that the river is full of rocks and tree snags. It was a rainy day so I don’t think Lewis and Clark could see that ½ of the mountain was missing. Boulders from the landslide were in the river and also up on the Oregon side as well. Lewis and Clark deduced that an earthquake had caused what they saw about 200 years before they arrived. That would have been approximately 1600 since they were there in 1805.
It should be noted that the old Indian legend of “The Bridge of the Gods” could have some truth to it, as the landslide debris could have formed a natural bridge across the Columbia at that time, which made it possible for the Indians to cross on dry land. Later the dammed-up material washed away. To this day the highway crossing the Columbia at Cascade Locks is known as “The Bridge of the Gods”.
In the winter of 1997-1998, the area was pummeled by powerful storms that eroded away tons of sand and exposed the uncanny natural wonder of a hidden forest. Some geologists theorize that the ancient trees were felled during the major earthquake that hit the Cascadia subduction zone in 1700. The earthquake dropped the forested land into the tidal zone. When the ocean water rushed in, it buried the decapitated trunks in the mud and sand, which staved off decay and preserved the forest remains for years to come. That forest is known today as the “Neskowin Ghost Forest”.
That Cascadia subduction earthquake has now been tied to the Bonneville Landslide of 1700 in present area of Cascade Locks. So, Lewis and Clark were a hundred years off. Not bad if you ask me.
The Cascadia Earthquake caused a tsunami that killed many tribal people on the west coast. The tsunami also known as the “Orphan Tsunami” in Japan headed across the Pacific. The Cascadia Earthquake happened at 9:00 pm on January 26th, 1700 Pacific Time. A tsunami reached Japan at midnight (Japan Time) 4792 miles away. That means it was traveling about 500 mph.
Today if you visit the Bonneville Dam site there is a plaque that reads that the Bonneville landslide took place 1400 years ago around AD 600 which we know today is about 1100 years off.
The forensics that went into this whole Cascadia subduction/Bonneville Landslide incident I find fascinating and intriguing.
For the Boring Volcanoes we point out a few as we drive though Boring, Oregon. I had lived in the Boring/Gresham area for over 30 years and had never heard the term ‘Boring Volcanoes’. They get their name from the area they are found in which in turn gets its name from a homesteading family in the Boring area: the Borings. Steve Hayley went to school with one of the Boring descendants. It turns out nearly every little hill or mound in the greater Portland/Vancouver area was once an active volcano. There are about eighty total Boring Volcanoes ranging in size from Mt. Scott and Mt. Tabor to Hogan Butte. We have now worked Hogan Butte into our itinerary. It just goes to show you, you’re never too old to learn – it’s fun.