Monday, 19 October 2009

Cinder cones

Anyone visiting Mauna Kea can't help but notice the mountain is littered with cinder cones. They are the result of volcanic activity and form after the initial rift zone eruptions which is how Hawaiian volcanoes behave typically. Magma is forced to the surface through large weak points and creates fissures and some spectacular lava fountains. After this initial activity magma escapes through specific weak points and cinder cones are formed which mark where individual eruptions have occurred.

Their structure tends to be relatively weak and they rarely grow to enormous heights, a thousand feet is a rough limit. Towards the end of an eruption the lava often breaks through one side of the cinder cone resulting in a horseshoe shaped structure. The red colour is a result of water being heated by magma and escaping through the cinder as steam. This oxidises the iron in the cinder, essentially turning it to rust (iron oxide).

There's a spot a mile or so along the dirt road above Hale Pohaku where the tour buses nearly always stop to allow the visitors to take photos of the saddle (the part of the island between Mauna Loa and Mauna Kea - essentially a very large valley). This is actually really helpful for us as we often drive up to the summit at the same time the tour buses leave the Visitor Center for the same destination. They don't go as fast as we do although on the dirt road "fast" is a relative term! We always stick to the 25-mph speed limit of course...

Anyway, I'd never actually stopped at this spot before so took the opportunity to take in the view early on Saturday morning. The ancient cinder cones in the middle of the picture are now covered by vegetation so don't look so red these days! Above the cinder cones is the northern flank of Mauna Loa and its lava flows. The clouds are really just clouds and nothing to do with volcanic activity!

As ever, clicking on the pictures will give you a larger version.


Keera Ann Fox said...

These landscapes have such lovely colors in them. They look beautiful.

Did you ever think you'd be an amateur volcanologist when you took up professional star-gazing? :-)

Tom said...

Keera - I think I was eleven years old when we had a student teacher give us lessons about volcanoes. I was fascinated and still am these days.

Here's a coincidence - in that same class was a girl I've known since we were both 5 years old. She is now a volcanologist - in Hawaii!

Perhaps this is a bit of a surprise, but although I have a love of astronomy and volcanology (actually, physical geography more than volcanoes), what I really wanted to do when I was 18 was oceanography - and I would love to return to university to study that subject one day!


Keera Ann Fox said...

So you're out of your depth, then. *ducking and running like h---*

Just had to make an oceanography joke. May I come back?

Thanks. :-)

It must also be nice to have someone who has known you from childhood and your home country actually physically near you.