Tephra

While enjoying and photographing episode 15 of the current eruption we got dumped on.

It was while photographing the spectacular fountains of episode 15 that bits of tephra began drifiting down on the crowded viewpoints along the crater rim. There was little wind and the enormous volcanic plume drifted over the eastern end of the caldera where thousands of people had come to view the eruption.

As I stood by the tripod I noted little clumps of Pele’s hair lazily drifiting down. Looking to see where it landed I note minute black gritty granules atop the camera and tripod. Oh lovely!

No hat or glasses, I had left these in the car. Pele’s hair visible on my camera gear, and a distinct gritty feeling in my hair… I had had enough, I had been photographing the high fountains for over an hour, I decided to call it and head for the car. I attempted to shake off as much as I could before driving home, not sure how successful that was.

Leaving the park and heading down the highway towards Hilo I run into a rainshower, no surprise. It is when I turned on the wipers that I was surprised. A substantial pile of debris is scooped up and depisited on on side of the windshield. Oh heck, I quickly turn off the wipers recalling that this stuff can badly scratch the glass if ground in by the wipers. I pull over to clear this mess.

While looking at the little pile of tephra on the side of my windshield I hesitated before I swept off. Thinking twice, I rummage in the car for the plastic container that had held trail mix a few hours before. I carefully scoop up as much as I can into the container… I want a better look at this stuff.

Getting back on the road I leave the wipers off in the rain… I can see through the drops. I let the thickening rain wash the remaining tephra away.

Now I just need a decent microscope with a camera mount. Just the thing sits at work, with a cell phone mount I made for that ‘scope.

The view in the microscope is revealing. Of course there is a copious amount of Pele’s hair, glassy golden fibers that are quite pretty in the microscope. In the sample I have these are becoming broken up by repeated handling. Much of these glass strands are more fibrous than I expected, in place of simple glass fibers there is instead a complex structure of fibrous appearing bundles.

Another surprise was the black gritty portion that had been so obvious when falling and getting in my hair. I expected bits with a broken rocky appearance, perhaphs a gritty sand like material. Instead I find glassy reticulite, little fragments of glassy foam thrown high by the eruption and light enough to drift the couple miles to where it fell on the viewpoints and parking lots.

Reticulite only forms in high fountains of perhaps 300m (1,000ft) or more, and this fountain certianly met that criteria. It is quite pretty in the microscope, something the photos here fail to properly capture. The fragments are mostly small, typically half a millimeter in diameter, with a few larger bits mixed in.

There are also blobs of glass, and other bits that are part Pele’s hair and part reticulite, sometime broken fibers embedded in the reticulite born of the violent conditions in the lava fountain. This stuff is facinating, need to do a little more reading on the subject.

While tephra does not usually fall in the main section of the park, it has been accumulating in large quantities to the west of the caldera driven by the prevailing easterly tradewinds. Piles of tephra can be found along the rim directly to the west of the current vents. I ran into a fair amount when hiking out in the Kaʻu Desert a couple months ago.

This is my second personal experience with falling tephra, the first was from Mount Saint Helens in 1980 when ash drifted into the Portland area a couple times, including covering my childhood home. Getting dumped on by the volcano again was an adventure, but not an experience I care to repeat.