Monday, 22 February 2010

Volcanic bomb

Another picture of a volcanic or lava bomb. This was from the same bomb field I wrote about the other day. The place is a geologist and volcanologist's dream, there are so many different types of rocks on the ground including a type of rock I can identify without looking it up - pumice. That's the bubbly type of rock you can see in a few places on the ground.

Like the bomb, pumice tends to be formed in violent volcanic eruptions. It's "frothy" molten lava that has a high gas and water content and when ejected in an eruption cools rapidly trapping the gases inside and forming "bubbles". The rock can be so light that it can actually float on water!

The ridge just to the east of Hale Pohaku is a bit of a mystery to me. Although I've known it was there for years I never bothered to walk up to it and have a look until now, but it has black sand, lava bombs, pumice and rocks that look as though they experienced some violence in the past. I'll try to find out if there's more known about it because it's certainly attracted my attention for now - speaking as a scientist of course!

One mystery is where the violent eruption took place. There's no obvious crater nearby but then again volcanic bombs and pumice can be hurled miles from the eruption site, so that brings a lot of possibilities into play. Just up slope, though, there's no obvious candidate.

Hey, me and my shadow! (to the bottom right).


Zuzana said...

I think it looks more like a strange nut like fruit.;)) I like your shadow.;)

Andrew Cooper said...

Thanks for the hint. When I got up Friday I needed to stretch a bit. A short walk to the lava bombs you describes was perfect.

There are indeed lava bombs everywhere you look. As for the crater? You are standing on it's rim. The next hill over is the other side. I walked to the next hill and it too is covered by the same material and lava bombs. I suspect the south side, downhill, was breached and destroyed by lava from the same vent as the eruption progressed.

Tom said...

Thanks, Andrew, it didn't even occur to me I was standing on the crater's edge! I'll take a closer look next time, perhaps from the dirt road above.

Zuzana - it's that strange shape which gives it away as a volcanic bomb!