[BR-Crater] New Year review of the Black Rock crater research

[Ian Kluft]

We only ended up having a couple trips to Black Rock for crater research
in 2009.  Though both were quite useful.  As I've done each January since
the theory started in 2007, I'd like to review what has happened in the
past year and set the agenda for upcoming study.

I'll jot down notes here.  Followup discussion can also contribute to the
annual review web page I'll make this month.

New geologist on the project
----------------------------

As 2009 began, the project had just gotten some attention from the Dec 2008
issue of Discover Magazine.  I was contacted by a retired mining Geologist
from Reno, Rich Loring, who contacted me after seeing the article.  He
expressed interest in the project.  Like any good scientist, he's not
jumping to any conclusions before evidence is found to support it.  (That's
a good thing.)

Updating theory from 60x40km ellipse to 87km circle
---------------------------------------------------

In January 2009, as I was preparing for the previous annual review,
I found the 87km (54 mile) diameter circle in the terrain around the
area.  The terrain features are so big and eroded that it's very
difficult to see.  When you scale up to see the whole outline, the
individual mountain ranges or significant changes in elevation in them
which consist of the outline are no longer visible.  It first caught my
eye on a far scaled-up view as a circular disturbance in the near-chaos
of the surrounding Basin and Range.  Zooming back in, the outline turned
out to include all of the highest peaks surrounding the Black Rock region
and various mountain ranges that are shaped in arcs that make parts of
the circle.

When I first met Rich Loring at his home in Reno, he had gotten the geological
maps for Washoe, Pershing and Humboldt Counties to compare against the outline
I observed in the terrain.  Unfortunately, we haven't found online copies of
these maps - they're more detailed than electronic maps we've found from USGS
and the State of Nevada.  Rich observed that putting these maps together,
there is a change in the geology of the region at this outline.  It's a useful
sanity check that the circular outline needed in order to continue to be
considered further.  As usual, this is not proof of an impact.  But it's
larger than any known volcanic caldera.  And calderas tend not to be circular
shaped at all the larger they get.  So for now it's "interesting".

The 87km ring also adds another interesting element to the research.  If
proven to be an impact, its diameter is just 3km short of the 90km Chesapeake
Bay Crater which is the largest known in the US.  The Chesapeake Bay Crater
is buried under 75m of mud and water.  Since the theoretical crater at Black
Rock is exposed at the surface, it would make it the largest crater you can
visit in the US.  And since it's already on federally-protected land, it
would likely become a popular site for formal geological studies.

Crater Assault 4 trip, April 26
-------------------------------

As the region dried out in the Spring, we made an exploration trip dubbed
Crater Assault 4 on April 26.
   http://www.stratofox.org/pics/sca4-200904/
It was a day hike at Pahsupp Mountain, on what now appears to be a ~30km
(20mi) concentric ring inside the 87km ring.  It's roughly the same distance
from the center of the 87km ring circle as the parts of the Black Rock Range
which we've already explored.  (Since the center point is on the playa in
the Quinn River Sink area, there's no exposed bedrock to find there.)
The first part of the hike was along an area that appeared to be a fault
line from the terrain.  We found a lot of "slickensides" which confirmed
the fault line, but was a terrible place to look for shatter cones because
they keep triggering similar visual cues.  Once we climbed over the ridge
away from the fault, I found some similar formations to what we found in
the Black Rock Range which look like low-grade shatter cones.  It's the
same "not good enough" we already had, but interesting to note.

I had already found in research that the kinds of high-quality "textbook"
shatter cones that geologists want to see are more likely if not exclusively
formed in fine-grained rocks.  The vast majority of the rocks in the areas
theorized to be pre-impact are coarse-grained.  So my original plan to try
to exclusively look for shatter cones as the shortcut to finding proof may
not be as good an idea as it first seemed.  The search for shatter cones
should continue because it's cheaper and the exploration adds to our
experience with the Black Rock region.  But I'm now coming to the conclusion
that we can't use that approach exclusively.  So in 2010, we also need to tap
our contacts among geologists for access to labs with electron microscopes
and pay for imagery.

Black Rock entry updated on the IFSG Impact Database 
----------------------------------------------------

In August I submitted the 87km ring as an update to David Rajmon of the Impact
Field Studies Group for the Impact Database.  It was included in the October
2009 update.  Black Rock is currently rated as a "possible" impact since the
theory is not proven. See http://impacts.rajmon.cz/IDhistory.html

Stratofox 6 trip, Oct 10-11
---------------------------

We had another exploration trip to Black Rock dubbed Stratofox 6 on Oct 10-11.
We piggybacked some crater research with the Stratofox team training event.

Rich Loring was able to join us for another tour of the area.  We planned to
give a similar tour as we gave to geologist and planetary scientist Bob Verish
a year earlier.  But as an informal tour, it quickly went its own way led by
Rich's own questions and curiosity.  One conversation which I've now come to
expect with every geologist went along these lines...  Rich pointed at the
mountains of breccia east of Upper High Dry lakebed and said he could tell
(from literally a mile away) it was a volcanic breccia.  So we went there to
take a look.  When he saw the "inclusions" in the breccia were jagged, not
rounded, he considered that the possibility of an impact scenario remained
open.  I previously had similar conversations with Bob Verish in 2008 and
Brad Douglas in 2007.  These are apparently conversations and observations
we must expect and allow to run their course when introducing geologists or
anyone with geology training to the area.

After Rich returned home, Tom, Andrew and I hiked the next morning to the
south from Upper High Dry to an area of the Black Rock Range we haven't
explored before.  The entire route was up in the breccia rocks which we
observed overly fractured rocks in the entire southern Black Rock Range.  We
reached the pass overlooking the Black Rock playa, our exploration was cut
short by an approaching dust storm.  Next time we'll try climbing up into the
Black Rock Range from near its southern tip from the main Black Rock playa.

Photos from Stratofox 6 are at http://www.stratofox.org/pics/sf6-200910/

Conclusions
-----------

As I mentioned, I decided that searching exclusively for shatter cones
probably isn't quite the shortcut I hoped it would be.  We'll need to add
to our plans to hook up with labs for electronic microscope imagery.

Also, feedback I've gotten on the 87km ring indicates that many people don't 
have the interest (or probably also attention span) to look at the maps I've
made so far.  They just say "I don't see it".  I'll make a web page with more
detailed looks at each of the mountain ranges that are part of the ring, to
make that easier to piece together for the big picture.