Wednesday, September 08, 2010

ALF rock

Seeing pictures of ALF Rock on the Ron Smith website (Relics of the Ancients) , Norman Muller writes about the rock:

On that website from California are photos of a fascinating boulder with smaller rocks placed on top. These smaller rocks, possibly donations, are cemented in place! I assume they were fixed in place by the deposition of a mineral in solution washing over the stones over a very long period of time. You can see detail photos of the boulder and the smaller rocks by going to Ron's website (I sent you the link yesterday). ALF Rock is found in the Indians folder and under Crocodile Rock.

As a geologist, wouldn't you like to know what the cementing material is? And given the climate in this part of the U.S. wouldn't it be possible to figure out the rate of deposition? I would assume we're probably talking about millenia.
Herman Bender a geologist responds:

Some of the photos suggest that what we are looking at is exfoliation and differential weathering with moss or lichen covering parts of the weathered surface. If you look closely at these images, you can see that the gray color/texture is a weathered surface.
Norman then writes:

If you look at the images of Crocodile Rock, particularly the first one showing the eroded face of the rock, which has wave-like erosion at the bottom, just above that is a line of small stones eroding out. There is also a similar horizontal line of stones just below the top of ALF Rock (ALF Rock is in the same area as Crocodile Rock). I now believe that the rocks on top were an integral part of the boulder (a conglomerate), and that over time they became visible as the softer stone around them eroded away. Does this sound plausible?

1 comment :

Tim MacSweeney said...

Maybe some human shaping is going on as well. The angle of the photo made me think (big surprise), "turtle."
Maybe two...