Happy Halloween, everyone!
I’d like you all to meet my friend Barbie. Barbie works as a coastal geohazards investigator in the Pacific Northwest. Her job entails spending a lot of time outdoors along the majestic rocky coastlines of Oregon & Washington examining the risks for landslides, tsunamis, and flooding.
While she adores her time spent outside, here in the Pacific Northwest that does mean putting up with a lot of rain, so today she sported a cozy sweater, a white poncho and thigh-high, black mud boots. She also carried with her one of the tools of her trade, a soil core sampler which she took to a mud flat along the northern coast of Oregon this morning.
She wanted to share some pictures with you from her trip, but sadly her camera fell into the deep mud and could not be retrieved, so she had to rely on her iPhone to take the pictures now that she’s back home.
A small costal town hired Barbie to assess their tsunami risk, so she took her core sampler to the mud flats that abut the town’s southern border. There she twisted the corer deep into the thick mud and slowly pulled it out so that she could examine the layers of sediment. She actually did this eight times today, for each sample she moved further away from the oceanfront. Luckily, she brought the final sample back in her truck, so she could take pictures of it again from home with her phone. Here’s what she saw:
There are three distinct layers of sand in this sample which was taken hundreds of yards from the beachfront. She suspects that one of the top two layers was deposited by the tsunami that resulted from the 1964 “Good Friday” Alaskan earthquake. Though that quake didn’t originate nearby, it was enormous and produced ferocious tsunamis which affected towns far south along the Pacific coast.
That bottom layer of sand is the one she was looking for as a definite event marker. This large deposit she believes is the 1700 Cascadia earthquake. This event was local, and repeat occurrences are the primary long-term hazard concern for towns along the Pacific coast. She can’t be completely sure just from this soil profile that what we’re looking at is the 1700 event, but she noticed some old tree stumps partially buried in the mud near where she took this sample. Tomorrow morning she intends to call her friend dendrochronologist Ken to see if he can assess the year when those trees died. She feels pretty confident that he’ll find that growth stopped around 1700 as this landscape subsided during the earthquake, sinking the forest floor beneath the ocean waves.
Barbie suspects from this evidence that the coastal village which hired her is at great risk from tsunamis. In the coming weeks she’ll meet with local politicians, builders, and engineers to discuss the best risk mitigation tactics, and also to help the town develop effective escape routes.