(This is a repost of an article originally published July 12, 2010).
The latest Eruptions Word of the Day is "Tuya". So, what is a tuya? This is a tuya:
Alright, well, that doesn't entirely help, does it? Lets look at the feature the arrow indicates. Some observations:
It is low and broad.
It has a relatively flat top.
It is steep-sided.
If you look real close, you can see crudely columnar jointing in the some of the outcrops near the top.
If you had a piece of it in your hand, you'd know it was a volcano rock (andesite, very rarely you can find bits that are quite glassy).
And right next door to this feature is a reddish cone that is obviously a cinder/scoria cone.
So, what is it? How can you construct a flat-topped volcanic landforms with features that indicate a strong cooling gradient (columnar jointing, glassy ...
