[BR-Crater] trip report and pictures from Crater Assault 3

Tue Sep 9 15:49:24 PDT 2008

I've posted my photos from the Stratofox Crater Assault 3 event this past
weekend.  The point of this trip was to investigate the theory of a possible
impact crater at Black Rock.  As others' photos are uploaded, they'll be
added.
   http://www.stratofox.org/pics/sca3-200809/

Note that the upcoming Stratofox 5 trip to Black Rock on Sept 26-28 will
be for a different purpose: exploration and training.  There will be
exploration based on what the participants are interested in.  If you
aren't interested in the rocks, that won't be the focus of the next event.
Then again, if the participants are interested in some more of this,
it's on the menu.  It still won't be everything.

I really enjoyed this trip.  And it sounds like everyone else did too.
The attendees were...
   Ian Kluft KO6YQ from San Jose
   Heather Stern KG6ZYC from Campbell
   Lowell Gordy AF6BI from San Jose
   Tom White KG6BRK from Placerville
   Bob Verish from San Diego
   Moni Waiblinger from San Diego

Many many thanks to Bob for coming along.  With his geology experience,
we were able to learn much more about the area.

Some geology terms used below...
* breccia: broken, jumbled rocks re-cemented back together into a new rock
* dike: a vertical flow up or down a crack with lava, impact melt or
  crushed rocks that eventually turn to rock in the crack.
* jointing: a long straight crack sort of like a mini-fault, no debris in it

Summary of the trip
-------------------

Friday was basically a travel day.  We arrived in Gerlach at 5PM and
at camp about an hour later, including some stops along the way.  The
moon set early both nights revealing an amazing zero-light-pollution
clear night sky.

Saturday was the busy day to look around.
* Our first objective was a hike on one of the nearest slopes on the
  north side just to show Bob (a geologist with impact crater experience)
  the kinds of fractured rocks we've found throughout the area.
* Our second objective was up the 4x4 trail to the north in one of the
  areas I thought might be a place to look for shatter cones.
* We had lunch and a break at camp in the shade during the hottest part
  of the afternoon.
* Our third objective was to find the location from Stratofox 4 last year
  and show Bob where we found what appeared to be black obsidian-like rock
  that came down cracks in the rocks in "dikes".

Saturday's results were encouraging.
* We showed Bob the fractured rocks that we found are typical of the area.
  He pointed out aspects of it that we learned to watch for later too.
  Particularly, the "jointing" (mini-fault-like longer fractures) were
  just as significant as the smaller fractures in indicating that these
  rocks have been through a lot of stress.  He's actually not so interested
  in the thin fracturing unless jointing across it is also present like
  we saw here.  He observed that the fracturing appeared to be from stress,
  not from cooling and not in a fault zone.
* The hike for the second objective found more fractured rocks with jointing
  but seemed not to be getting closer to the center.  We decided on another
  location to add to the to-do list.  We found some breccias with large
  (inches) inclusions/clasts and at a distance thought we might have seen
  some with boulders for clasts.  Those would be called a megabreccia if we
  can get close enough to confirm.  (Megabreccias are considered likely
  evidence of an impact but not proof.)
* The hike for the third objective easily located the cliff face seen at
  Stratofox 4.  With Bob's help, we knew more of what to look for.  We found
  last year's location to be far more encouraging than we realized.  At times
  we were all trying to talk at once about the rocks we saw there.  We found
  the black igneous rock dikes, which did appear to come from above.  (That's
  what it should do in an impact, and should not do in a volcano.) We found
  places where the fracturing pattern showed an uncountable number of apexes,
  and some places where the fractures showed branching.  These are things
  that should happen in impacts.  Actually, since I couldn't stand far enough
  away on the steep slope, some of this became even more obvious in the
  photos.  For example, "a lot" of apexes in person became "uncountable"
  apexes when it stayed perfectly still in the form of a photo.

Sunday we broke camp and looked at some areas outside of Upper High Dry
on the way out.
* Our first objective was an apparent volcanic neck structure near Lower
  High Dry Lakebed.  Many of the rock structures in the area appear like
  volcanic necks.  The idea was to look at whether anything there might
  conflict with an impact, indicate volcanic activity following an impact,
  or something else.
* Our second objective was an area of more apparent volcanic necks which
  the geological map of Nevada listed as an area of basalt (a kind of lava).

Sunday's results were also encouraging.
* The apparent volcanic neck near Lower High Dry was not what it appeared.
  What should have been lava in the neck turned out to be yet another
  breccia, just with similar dark color to lava.  This is consistent with
  an impact as a potential breccia dike with some melt material.  But it
  is not a volcanic neck.
* On the way to the second objective, we noticed it was right next to the
  Confluence Point of 41N 119W so we went there first.  We got photos with
  our GPS receivers showing 41.00000 N 119.00000 W.
* The second objective was a lot of hiking on steep slopes of loose rocks.
  There were still more of the thinly-sliced fractured rocks with jointing
  across them.  (See the note below why this is significant.)  We also found
  that lake erosion from the period of Lake Lahontan must have been a factor
  here because many of the boulders from above were cemented in lake tuff.
* I need to let Bob pick the proper wording on this. But as I understand it,
  he determined the supposed basalt is not basalt.  It looks like shale but
  doesn't break like it.  It's appears like a kind of tuff.  Since it isn't
  basalt as the map says, the geological map of the southern Black Rock Range
  may have been made too hastily and needs to be reviewed.

One very important finding from this is the widespread area with the
thinly-sliced fractured rocks.  Bob pointed out there is also jointing
in parallel mini-fault-like straight cracks across the fracturing.
That indicates the fracturing is from a source of stress, not from
cooling.  And it isn't a fault zone.  We found these kinds of rocks
at Upper High Dry and locations a couple miles north, south and west
so far.  (I had to check the photos from Stratofox 4 last year to
confirm it's also to the south.  We didn't go there this time.)

Initial conclusions
-------------------

So the on-the-ground observations give us have a pretty good picture that
an event on the scale of more than just miles across occurred there which
fractured the rocks similarly across an enormous area.  That should help
get more scientists to take this seriously as something to look into.

Some of the photos may contain possible low-grade shatter cones and
will need more review.
   http://www.stratofox.org/pics/sca3-200809/img_1618.jpg
   http://www.stratofox.org/pics/sca3-200809/img_1619.jpg
   http://www.stratofox.org/pics/sca3-200809/img_1620.jpg
   http://www.stratofox.org/pics/sca3-200809/img_1624.jpg
   http://www.stratofox.org/pics/sca3-200809/img_1625.jpg
   http://www.stratofox.org/pics/sca3-200809/img_1627.jpg
   http://www.stratofox.org/pics/sca3-200809/img_1629.jpg
   http://www.stratofox.org/pics/sca3-200809/img_1632.jpg (best candidate)

If any of those pictures turn out to be confirmed as shatter cones,
then that alone would be proof of an impact.

Overall, it was a very successful trip.