Friday, July 17, 2015

In My Own Backyard

One of these pictures was shot on the Big Island of Hawaii, one was taken at the Trail of Two Forests south of Mount St Helens, in Washington.  Can you tell which is which?

Here's an explanation of what you are seeing in these photos:

Hot lava flows around a standing tree, which erupts in flames, but cools the lava sufficiently for it to harden.  The tree burns away leaving a hole. 

Cooled lava like this is called basalt. The landscape of Hawaii, currently growing from the eruption of Kilauea, is just a fresher version of similar rock in the Pacific Northwest. There is a lot of basalt in the Hawaiian Islands, but we have a lot of basalt here, too!  Much of ours came from huge vents in what is now eastern Oregon and Washington. That lava flowed east into Idaho and west all the way to the ocean.

The lava around Mount St Helens came from, yes, eruptions of Mount St Helens.  The other thing that Mount St Helens spews out is ash, and there is a lot of that too.

Where slides have occurred near Kalama Creek, it is easy to see that there is a whole lot of ash under the duff of the forest floor.

At one new section of the trail, we came across these little ash towers.  Each tower has a little rock or pebble on top, protecting the ash directly underneath from erosion.  This is a similar phenomenon to the creation of  the "goblins" of Goblin Valley and many other formations in southern Utah: a erosion-resistant cap on top of a less-resistant base underneath.

Going back to our lava flows above, what happens if the tree in the way of the lava is not standing? Well, you might get something like this:
A tunnel where the downed tree once was.  At the Trail of Two Forests, it is possible to descend a short ladder and crawl through this tunnel, which must have formed from two downed trees that were immersed in lava.  The tunnel is open at each end, but crawling through requires a sharp turn (and knee pads if you are as old as me.)

Oh yes, and the top picture above was taken in Volcanoes National Park on the Big Island of Hawaii.

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