Field Trip, Finally

The mineralogy class I T.A. for finally got out into the field this weekend.  It wasn't the two-day, fully-loaded, mandatory trip originally planned, but it also wasn't -4 degrees F and snowing either.  We had a good time visiting outcrops in the Butte area with a small group of dedicated students.

Stop 1.  Boulder Batholith.  A lovely biotite granite.  This outcrop was very weathered - the power of rock crumbling at your touch! - note the grus (weathered granite) debris at the base of the outcrop.  Also nice exfoliation and spheroidal weathering.

 Above, left: Granite of the Boulder Batholith.  Above, right: Weathering in the batholith.

Stop 2.  Rader Creek Granodiorite.  An older, slightly more mafic intrusion.

Stop 3.  A skarn associated with the batholith.  Mineralogy includes garnet, calcite, tremolite and epidote, as well as possible apatite and rhodochrosite.

 Above: Skarn minerals (brown is garnet).

Stop 4.  An abandoned railbed passing through the contact between the Boulder Batholith and older Elkhorn Mountain volcanics.  Along one segment the railbed is built on what appears to be mine tailings (no shortage in and around Butte!).  The students enjoyed scrambling along the steep incline looking for nice sulfides - mostly pyrite and bornite.  One sample found also contained a bit of malachite.

Above, left: View of the Tobacco Roots from Stop 4.  Above, middle: sulfidic minerals of the tailings that form this rail crossing weather yellow.

Above, right: Students hunt for sulfide minerals on the steep slope.

Stop 5.  Ringing Rocks is located on BLM land.  Our 15-passenger van did fine on the good dirt road (including the last little bit with rough road and a steep drop off the hill).  The reward is pile of gabbroic boulders (containing lovely little blue labradorite grains) that are perched just-so.  When struck with a hammer, each boulder emits its own ringing note.  It would be fun to get a crowd to play out a short melody.

Above, left: Sign at Ringing Rocks.  Clearly, this formation came together very quickly!  Above, middle: Mineralogy students make noise.

Above, right: View of the Anacondas from atop Ringing Rocks.

Stop 6.  Our adventurous crew headed for a Proterozoic/Archean exposure in the Highland Mountains.  Here we found intermediate-mafic garnet-bearing rocks exhibiting class melt-reaction halos.  Lovely!  We were well-timed for a gorgeous view of sunset on the Tobacco Roots. 

Above: The setting sun glows on the Tobacco Roots, as seen from the Highlands.

The Missoulian, September 27, 2009

The story I find most interesting this week continues to be the local wildfires, particularly the Kootenai Creek wildfire.  The Missoulian had two updates today, here and here.  I had been on a field trip yesterday; when returning along I-90 smoke from the Kootenai Creek fire was obvious in the Bitterroot Valley to the south:

Smoke from the Kootenai Creek fire.  View from I-90 E.  Downtown Missoula is just barely visible above the trees on the left side of the photo.  Stevensville, the town nearest the fire, is a little more than 30 miles from this vantage point.

When I got home I decided to go out and take a few pictures.  I traveled south on Route 93, which follows the Bitterroot Valley.

The view from Lolo, just south of Missoula.

As I got closer to Stevensville, the clear, blue sky was no longer visible.  What appears to be a cloudy or overcast sky is entirely smoke.  The plume of smoke continued from here across the valley to the east.  The mountains on the east side of the valley were either extremely hazy or entirely invisible.

I drove only a couple miles or so beyond this sign.  It was late, I was tired, and I didn't think I needed to see too much more.

I pulled off Route 93 to take this photo (below), and then I headed home.  Again, this fire was sparked by lightning in early July.  I can't imagine being one of the residents dealing with this.  When I stepped out of my car, it smelled like the biggest campfire ever.  Their hair and clothing, their homes, their cars - everything must be invaded by the burning smell.

The horses didn't seem to mind.  This photo was taken just south of Florence, about 3.5 miles north of Stevensville.

Pre-evacuation orders have been given, and some livestock have been moved, but there is no mandatory evacuation now.  As you'll see from the links above, firefighters are optimistic for the cooling weather and a shift in wind direction.

Field Trip to Glacial Lake Missoula

Last weekend (September 12) I enjoyed the first of many weekend geology field trips scheduled for the fall semester.  This field trip was part of the Winston-Thompson symposium, honoring UM Department of Geosciences professors emeriti Don Winston and Gray Thompson.

So, those of you in the know (um...GeoGuppy?) will wonder if I've taken possession of a time machine, as Glacial Lake Missoula no longer exists.  Much like the former Glacial Lake Hitchcock in the Connecticut River Valley or Glacial Lake Cape Cod in Cape Cod Bay, Glacial Lake Missoula was created during the Pleistocene period when the advancing Purcell Lobe of the Cordilleran ice sheet dammed the Clark Fork River (which runs through Missoula) near Pend Oreille, Idaho. The impounded river, as well as some of the melting ice, filled the valleys from Hamilton to Polson.  At its greatest extent, GLM had a depth of 600 meters and occupied a volume of 500 cubic miles!

http://vulcan.wr.usgs.gov/Volcanoes/ColumbiaPlateau/summary_columbia_plateau.html

Of course, most of you are probably more familiar with GLM as its waters were the source for the floods that created the channeled scablands of Washington and Oregon.  See Nova's "Mystery of the Megaflood."  Of the many scientific controversies surrounding GLM, the number of "megafloods" produced is probably the greatest.  It is thought that the lake filled and then catastrophically drained multiple times.

So, our field trip was to visit the many landforms and deposits found in the area once occupied by GLM.  Sadly, we are too many hours away from the scablands to have visited those - a different trip, perhaps.  We also did not visit the mega-ripples created as waters catastrophically drained westward, but I understand that they are more spectacular in aerial photographs and maps than from the ground.

What we did visit: diamictite deposits (clay, silt, and gravel) interpreted as glacial till due to the presence of striated boulders, overlain by paleosol (ancient soil), then silts with climbing ripples and layers with syn-sedimentary deformation, and finally laminated layers (interpreted) as varves, with dropstones.  Was that a sentence that made you go, "hmmm....?"  What we saw: the gravelly deposits of an advancing glacier, followed by soils, and then by thin layers of sediment that were deposited in a deep, quiet lake.  Those layers have "dropstones," literally pebbles and cobbles that dropped through the water from icebergs floating in the lake.  We also visited an area of the lower Flathead River thought to be where floodwaters burst through a canyon, depositing rock debris.

Photos: Top, left: The group at an "outcrop" of unconsolidated sediment north of Arlee, Montana.

Top, right: Diamictite overlain by fine sediments; note soft-sediment deformation at elbow level; also climbing ripples; grading up into varves.  Bottom: Striated boulder in diamictite allows for interpretation of glacial till.

The weather was lovely (80+ degrees, clear, blue skies) and there were dozens of happy geologists to share it with.  The field trip was followed by a barbecue at Professor Winston's legendary home along the Jocko River.  As I have summarized for those of you on facebook, we enjoyed: beer, bison burgers, a bonfire, and banjo music.  It was great company, a beautiful, warm night, and good music (the banjoist was accompanied by guitars, bongos, flute, and cello!).

Photos: Left: The Lower Flathead River as it flows away from the Kerr Dam, south of Flathead Lake.

Middle: Dropstones in varves.  Right: Geologic hoe-down around a campfire.

The next field trip: A geomorphology class data collection trip to the Mattie V Creek.