Friday, April 9, 2010

Volcano Vocab: Guyot

I don't want to steal the thunder of any of the Skepchicks (especially Evelyn, who's doing a fantastic job on the Geology Word of the Week feature), but I thought I'd start a bi-weekly post on obscure or specialized volcanology words. (Yes, it's really just an easy way for me to post, since I've got the Glossary of Geology sitting here and all I have to do is flip a page to get a post idea, but I'll try to include a little discussion along with the posts.) We'll see if I'm any more successful with this weekly feature than I was the last time.

So what's the first word o' the half-week? By dint of me opening to the glossary of a volcanology textbook and pointing blindly: Guyot!

A guyot ("gee-oh") is basically a flat-topped seamount, or underwater volcano. The glossary in Bardintzeff & McBirney's Volcanology (2000) adds a bit about why it's got a flat top:
A submarine volcano with a flat top produced by wave erosion before the island was submerged. 
A guyot is one of the stages in the life cycle of an ocean island volcano, and the form occurs when a volcano is no longer actively growing and unable to replace what is lost to the erosive force of wind and waves. Here's a diagram to illustrate:

(This came from a powerpoint someone gave me a while back, and I don't know where they nabbed it from - looks like a textbook. If anyone recognizes it, let me know and I'll put in an attribution!)

Unfortunately, it's a bit hard to show off a photo of a guyot, since they're generally underwater. Here's something that looks similar, however, from Hawaii's Big Island. These photos were taken somewhere along Rt. 11 (Mamalahoa Highway) on the way to Punalu'u Black Sand Beach and Ka Lae (South Point).  I remember that there was some discussion going on about guyots, but I'm not sure if these are the real item. Does anyone else know if these are 'stranded' guyots?


ptrk said...

Looks a lot like a Tuya! (table top mountains common in Iceland) but without the glacier. How important is the choral component to the definition? Could a Guyot be a Guyot without the reef? Cool stuff!

Jessica Ball (AKA Tuff Cookie) said...

It does! (Too bad you missed the Pegrum yesterday - tuyas were the topic du jour.)

Maybe the reef part is just sort of a symptom of a lot of volcanic islands being in warm water? I'd have to read up on other guyots...

Garry Hayes said...

My understanding is that these hills are eroded scarps at the head of an old landslide on the flank of Mauna Loa. As far as seeing guyots, I think we have some of them in the Sierra Nevada foothills, but seeing as they got subducted, baked, squished, highly deformed and faulted, they don't look like guyots anymore!