Monday, January 23, 2006

A stream in the Valley of Desolation on Dominica. The rivulets coming in from the left are full of minerals that deposit black stains on the rocks, while the stream on the right looks like nothing so much as a river of alka-seltzer.

This place stank of rotten eggs and howled like a demon. Posted by Picasa

5 comments:

SerenitySprings said...

That is so beautiful. But how does it work? How can two streams so close together be that different? Science me up.

Dave-o-ramA said...

Well, you've got superheated water pushing through rocks of different kinds. The water is further saturated with things like H2S (hydrogen sulfide) and S02 (sulfur dioxide), both of whom in aqueous solution form sulfuric acid (H2SO4), which helps the already super-hot water to disolve minerals out of the rocks. The black probably comes from disolved manganese compounds precipitating out of the water, and the white minerals in the other stream are from different minerals.

This is similar to the 'black smokers' and 'white smokers' found in undersea volcanic vents along the mid-ocean ridges (just in a slightly different geologic environment, and on a smaller scale).

SerenitySprings said...

So how did rocks that different come to reside so close together? And is it normal for differing rocks to exist like this?

Dave-o-ramA said...

Not all rocks are the same. Some are different. Otherwise, there wouldn't be 'rocks' but just 'rock'. If all rocks were the same, we'd probably get screwed, and end up with all of our rock being Phil Collins or Michael Bolton.

Actually, this is on the slopes of a big volcanic complex. You've got deep-crustal rocks coming up with magma, plus shallower rocks of both igneous and sedimentary origin all getting jumbled together. This area is very active geologically, so lots of different kinds of rocks get all mixed up.

SerenitySprings said...

Unless, of course, you're me - then you just rock all the time.

Speaking of rocks, I kicked ass on my geo test today. Finished that baby in 7 minutes flat.