|Sugarloaf Rock at Cape Mendocino. Somewhere out to sea beyond the cape is where the Cascadia Subduction Zone is being destroyed, bit by bit.|
And you might want to be careful what you wish for anyway...
As mentioned in previous posts of this series, the Cascadia Subduction Zone is a spot where oceanic crust of the Pacific Ocean is being driven beneath the North American continent. The subducting plate, the Explorer-Gorda-Juan de Fuca is one of the smallest crustal plates on the planet. And it is being subducted faster than it is being created. It is indeed being destroyed...at the incredible (geologically, anyway) rate of a couple of inches per year. It will take tens of millions of years to consume the remaining plate material. When it is consumed, the subduction zone will cease to exist. The good people (or whatever species has evolved by then) of Portland and Seattle can stop worrying about subduction zone earthquakes.
As for being careful what you wish for? As the subduction zone is being progressively destroyed, it is replaced by the newly formed San Andreas fault/transform boundary. Although the San Andreas fault can't cause earthquakes as powerful as the subduction zone shakers (they top out at around magnitude 8.0, about 1/30th the energy of a magnitude 9.0), they are capable of serious mischief, as the quakes are often shallower, and that's a bad thing. The tragedy at Haiti a few years ago is a horrific example. The magnitude 7 quake killed nearly a quarter million people, despite having only 1/30th the energy of a magnitude 8 tremor. The focus was just a few miles deep.
|The beach and sandbar at the mouth of the Mattole River, one of the very few undammed rivers in California|
|Crowded Mattole Beach|
This is one of the most geologically active corners of California, and California as a whole is a very geologically active place. Mattole Road is winding and steep because the land here has been uplifted very quickly, and the intense rainfall erodes the mountains at an astounding rate. Honeydew is one of the wettest places in the state with rainfall in some years exceeding 100 inches (2,550 mm). The dark rocks in the picture above are former sea stacks (small rocky islands) that were lifted up out of the water by the recurring earthquakes that raised the shoreline by a couple of inches or feet every couple of decades. A particularly damaging quake took place in 1992, the magnitude 7.2 Petrolia event.
We took a leisurely day exploring the beautiful coastline before grabbing some dinner in Fortuna and heading back to the campsite in Humboldt Redwoods. We would head north in the morning.