A forest drowned by an earthquake
At low tide on the beach at Neskowin, Oregon, the remnants of a Sitka spruce forest appear in the surf. Roughly 100 ancient stumps, dated by radiocarbon methods to be about 2,000 years old, dot the shoreline. These are the remains of trees that once stood 150 to 200 feet (46 to 61 meters) tall. Until the winter of 1997-1998, the ghost forest was a local legend, with the stumps only appearing sporadically every few decades before being buried again by sand. A series of powerful El Niño storms during that winter washed away the sand that had concealed the forest for centuries.
The leading theory for the forest's demise points to a massive earthquake on the Cascadia Subduction Zone, a 600-mile-long fault that stretches from Northern California to British Columbia. The quake caused the land to abruptly drop, submerging the forest in the tidal zone. A subsequent tsunami likely buried the now-dead trees in mud and sand. This oxygen-poor environment preserved the stumps, preventing the normal process of decay. Scientists can see evidence for this sudden burial in the soil still clinging to the roots. An alternative theory suggests a more gradual process of sand dune encroachment over decades buried the forest.
Tree rings as seismic records
The Neskowin Ghost Forest is a strange landscape; is a paleoseismic record. Scientists use dendrochronology—the study of tree rings—to understand the history of seismic activity in the region. The stumps at Neskowin show that the trees, some of which were 200 years old when they died, all perished at the same time. This simultaneous death points to a single, catastrophic event rather than a slow rise in sea level.
By studying ghost forests up and down the Pacific Northwest coast, researchers have identified a pattern of large-scale earthquakes occurring every several hundred years. The most recent major Cascadia earthquake occurred on January 26, 1700, an event precisely dated by cross-referencing tree ring data from ghost forests in Washington with Japanese records of an "orphan tsunami" that struck their coast without a locally felt earthquake. The Neskowin stumps record an even earlier seismic event from around 2,000 years ago. This data helps geologists forecast future seismic hazards in the tectonically active Pacific Northwest. Today, the stumps themselves have become small habitats, encrusted with barnacles and mussels, and their eroded centers can form temporary tide pools for crabs and other sea life.