|
A Stratofox expedition went to Black Rock on our continuing theme of
exploration and familiarization with the region.
This was the second one which also explored a theory of impact craters
at the Black Rock region, visiting a place we nicknamed "Donut Basin"
because of the shape of the valley.
Though not pictured, we also saw a petrified forest and part of the
pioneer wagon trail route.
Images are in four subdirectories:
Jim Dennis KG6ZXF (Heather's husband) also participated but didn't
take photos.
Background information
See also the
message from the Stratofox announcements mail list.
We'd like to acknowledge Joey Carmosino KC6WBI
of the BLM Winnemucca Field Office
for pointing out that universities have been researching a petrified forest
near a theorized volcanic caldera.
We found some information at the universities' web sites.
We found additional geological summary info at the web site of the
Nevada Bureau of Mines and Geology at University of Nevada, Reno.
We had spotted the circular feature on satellite imagery in January.
It took a little research to determine it's the same place Joey was
referring to. Putting those pieces together increased interest in
visiting the location.
The circular valley was described as a "failed caldera" in a 1970's paper.
Since then it seems other geologists have just cited that paper but not
visited the site.
The theory didn't sound right to us.
There are no other examples of volcanic calderas
failing to collapse after get started.
That was the area we explored on the June 2 trip.
The site doesn't seem to have a name, at least not that we could find.
The 1970's paper and others that cited it described the location as
a "donut-shaped" basin.
So we nicknamed it "Donut Basin".
And the circular hill in the center is nicknamed "Donut Hole Hill".
We don't have anywhere near enough information to make any firm
conclusions.
But we already found enough to cast serious doubt on the site as a volcano.
There are layers of sedimentary rocks near the top of Donut Hole Hill
which Brad says are the kind that would be formed at the bottom of
an ocean.
As an impact site, it would be plausible to find those kinds of rocks
in the central uplift.
But as a volcano, there's no plausible way for ocean-bottom rocks to
find their way to a central cone in a caldera.
Though there could be other explanations for a circular geographic
feature - so that's why there isn't enough to make conclusions yet.
|
