Wednesday, April 3, 2013

Geo 365: April 3, Day 93: Invasive Dike at Seal Rock

Jumping over to the coast, this is at Seal Rock State Park, the southernmost recognized spot where the Columbia River Basalt (CRB) flows reached the area of the modern coastline. To anyone with a background in geology, the phrase "intrusive lava" should sound like an oxymoron, but it's actually fairly easy to find along the northern Oregon Coast. When CRB flows reached the Miocene coastline, they invaded the underlying unconsolidated sediments, forming dikes such as the one we see here.

My mind spins when I try to imagine the implications of this and related landforms- I struggle to picture the landscapes it suggests. It implies that the Coast range simply didn't exist, only 16-18 million years ago. That alone is difficult to picture. It implies a lava flow capable of reaching a length of 400-500  miles, with a high enough temperature and fluidity that it was still able to intrude into wet, semi-solid sediment quite deeply. Again, hard to imagine. Finally, this area would have been ecologically much like today, perhaps a bit warmer- the Oligocene in Oregon was a transition period from a more tropical climate toward the modern temperate climate. Obviously, the flora in the path of the flow had no chance. But the panic and chaos among the fauna at the time, as the fiery flood arrived, is terrible to contemplate.

As I used to say to students about quite a number of disastrous geologic phenomena, "It'd be quite the sight to see. From low orbit."

Photo unmodified. March 8, 2012. FlashEarth Location

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