Ghosts and Orphans
The Solving of a Geological Mystery
Like many rock geeks, I have a list of geological locations and events I have long hoped to visit and see. These include Þingvellir in Iceland (where one can walk from North America to Europe by crossing their plate boundary), the green sand (the mineral olivine) beach on the Big Island of Hawaii, the K/T boundary (which marks the end of the non-avian dinosaurs), and flowing lava. Last week, I had the good fortune to visit one of my sought-after locations, much closer to home, the Ghost Forest of Copalis Beach, on the Pacific Coast of Washington. Not only an amazing story of geology but also a mystery that had remained unsolved for almost 300 years.
First observed in the 1850s, when botanist James Graham Cooper described groves of dead cedars killed by “a gradual, slow sinking of the land…[that] has caused the overflow of the tides,” the standing dead trees weren’t studied by geologists until the 1980s. They had been prompted by the convergence of two lines of knowledge. The first was gleaned from earthquakes in Chile (1960 - Magnitude 9.5) and Alaska (1964 - Magnitude 9.2). During those quakes, two of the biggest ever recorded, coastal land dropped by a meter or two, which allowed salt water to inundate the lowered land and kill the forests. The second line was a better understanding of regional plate tectonics.
Out on the coast, two plates converge—the east diving Juan de Fuca and the west trending North America. Most of the time they are locked together like two giant pieces of velcro but every so often the velcro slips, creating a break, or earthquake, which in turn can generate a wave that spreads at 500 mph. This area of weakness is known as the Cascadia Subduction Zone.
Although no written records exist from the Pacific Northwest, we have more than three dozen Indigenous stories, as well as art work, ceremonies, and place names that reference Cascadia quakes. These stories do not provide an exact time but illustrate the enduring legacy of massive earthquakes and how they have long played a role in the culture and community of the region.
We do though know the time of the last great movement of Cascadia: 9PM on Tuesday, January 26, 1700, and estimated to be between magnitude 8.7 and 9.2. We know because tsunamis struck at least six harbors in Japan, killing several people and destroying many homes. No one knew the origin of these orphan tsunamis until Japanese geologists connected them with Cascadia 300 years after the events. Together with colleagues in the US, the Japanese researchers nailed down the precise timing of the rupture by studying written records, tree ring data from the standing dead copses, and sediment deposits to pinpoint the origin of the tsunamis and the ghost forests, which had died in the years following the quake.
The solving of these mysteries of the trees and waves is certainly one of my favorite examples of paying attention, being curious, and asking questions. Plus, it never hurts to root around in old books and records; you never know what stories you’ll unearth.
I have long been fascinated by the intersection of geologic time and human time. It is during these moments, with events such as volcanic eruptions and earthquakes, that we are reminded of the geological world we inhabit. Despite what some think, or hope, we are neither apart from or masters of the natural world around us. Geology has long shaped the story of humanity and will continue to do so. It would be great if we could have the humility to learn from the past and work to create a future that acknowledges that the clocks of our lives and planet Earth are wound together.
Wishing everyone a happy Solstice next Wednesday, the 21st. By the way, did you know that the sun sets today about 4:18PM and that it began setting at the time (give or take a few seconds) on December 5 and that sunset on the Solstice is 4:20PM?
Also come to Connecticut. The CT river valley is composed of two continents, or fragments of two.
Man I love this topic. I've often thought a great archeologic investigation would be to dig around at the estimated Tsunami high water above known inhabited locations in Puget Sound. My theory is that possessions, or parts of canoes or long houses and the like should be found up there, now far from the shoreline.