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

[Ian Kluft]

On Tue, Sep 09, 2008 at 07:08:09PM -0400, Brad Douglas wrote:
> Again, the "thinly sliced" rocks are neither from volcanic cooling nor impact.  They are created by successive freezing and thawing, which is often extreme in NV:
> http://commons.wikimedia.org/wiki/Image:Weathering_freeze_thaw_action_iceland.jpg

I have to be open to discussion of alternative explanations.  But I wish
you'd find a less confrontational way to present yours.

Compare that image with these from Black Rock just from this trip.
   http://www.stratofox.org/pics/sca3-200809/img_1602.jpg
   http://www.stratofox.org/pics/sca3-200809/img_1603.jpg
   http://www.stratofox.org/pics/sca3-200809/img_1606.jpg
I can dig up many more examples from previous trips too.

I can make several observations of differences between these rocks.
The biggest thing that stands out is that the cracks on the Iceland
rock image aren't even parallel.  There's a rough trend more or less
in one general direction, but not comparable.

The "thinly-sliced" rocks at Black Rock...
* exhibit highly straight and parallel fracture lines over wide areas
* are often cross-cut by sets of jointing which are parallel among themselves
* sometimes can be found next to other thinly-sliced rocks which are parallel
  among themselves but in a different direction. (So it isn't just upturned
  layering.)

When different sets of parallel-among-themselves fractures are next to
or crossing each other, we have made multiple observations that the
parallel lines in that area are all about a single axis.

The ones we saw Saturday were about an axis pointing up and to the
northeast.  Ones I found further up the hill in June of last year were
about an axis pointing also up and to the northeast.  Those observations
were hundreds of feet apart up/down the slope.

There's a surprising amount of complexity and structure to the fracture
patterns of the rocks at Black Rock.

Though the single photo from Iceland isn't much to go on, I can tell that
none of these observations will be possible because of the lack of highly
parallel lines.  It isn't the same thing.