You'll recall that our sixth day in Torres del Paine National Park had us hiking east from the Paine Grande Lodge. We hiked up over a ridge dividing Lago Pehoe from another turquoise-colored lake, Lago Nordenskjold:


At the so-called Italian Camp, we dropped our packs, and went for a small side hike. We turned to the north, and hiked up the French Valley:

The object of this day-hike was to see some glacier calving. The French Valley is famous for this: you sit back and watch, and big chunks of ice spall off the glaciers, crashing hundreds of feet below onto the rocks. A few seconds later, a sound like thunder reaches you: it was this that we came to experience.

Anybody seen a glacier around here? Rumor is that it was JUST here!

[The line demarcating vegetation above from bare rock below shows former height (and presence) of the glacier.]

Here's a look at the amphitheatre where our glacial show would be performed:


As the clouds cleared a bit, we could see an astonishingly thick cornice of snow/ice atop the mountain peaks. All the valleys up top had been filled in and smoothed off, and there was this white rim atop the black rock. The cornice is probably 40-100 feet thick in this photo:


An annotated photo of the area where we were observing the action:

What happened here was that a much larger glacier (see the vegetation line back a few photos) ablated away, splitting into two upper disconnected feeder glaciers, and a lower glacier which is now semi-buried in rocky debris (talus) and ice spalled off the upper glaciers.

A closer look at the annual growth layers revealed in the lower part of the glacier:


We soon saw some calving events. They were quite cool. Big booming noises, ice explosions seen through binoculars, eating chocolate and almonds. We were happy. Then we heard a roaring noise, like an airplane going overhead. We looked at the glaciers: nothing. What was making that noise? Then, from above, we saw it: coming down out of the clouds was a huge billowing white mass. Apparently, it was coming down from the cornice of snow atop the mountain. An avalanche! An honest-to-goodness avalanche! I have never seen one before; I was giddy at the spectacle. It looks just like a turbidity current, people, but it is white!

It was a magical thing to witness: watching it spread out and poof outward in hundreds of little round turbulent vortices. Everyone in the valley cheered: "YEAHHHH!!!!!"

Tough act to follow... but: Just east of us were the rugged Cuernos del Paine, a series of glacial horns made more photogenic by the pink stripe running through their middles, like a WWF Championship Belt:


This pink stripe is a granitic intrusion, approximately 12 Ma (Miocene*). Here is another photograph of the Cuernos, where the granite is very obvious:


We walked along the north shore of Lago Nordenskold towards the Cuernos campground...


Across the lake, some nice folds were visible:


The Cuernos campground is in this little nook. A lovely place to spend an afternoon and our final night in the park:


And it has very nice views of the Cuernos del Paine:


Seeing the Cuernos was the fulfillment of a decades-old dream for me. I think I saw them in an REI catalog (or perhaps a Patagonia catalog, hmm?) back when I was in college, and thought, "Wow. There's a place on Earth that really looks like that? I gotta go... someday." What I didn't expect then, and was pleased to see now that I was there, was the excellent evidence of stoping, one of the processes by which magma chambers enlarge their size and intrude into other rocks. Stoping is where chunks of the wall rock ("host rock" or "country rock") are broken off by inquisitive fingers of magma, and the liberated blocks (now xenoliths) drop into the magma chamber. Here, you can see (white arrows) some of these splurtles of granite working their way into cracks at the top of the magma chamber:


If these fingers of granite connect up, they separate the block of rock beneath them from the country rock (a form of physical weathering, like root wedging!). More dense than the surrounding magma, the resulting xenoliths sink. If the magma is still rather fluid, the xenoliths may now pile up on the floor of the intrusion. If it's getting to be mushy and semi-crystalline, their downward flow may be retarded, like a slice of banana trying to sink through thick oatmeal. As the granite crystallizes into rock, those xenoliths will be trapped somewhere between the ceiling (source area) and the bottom. Check out the diversity of xenolith positions (white arrows) displayed on this Cuerno:


Great looks at stoping here: some have fallen, some are still beginning to fall. I could easily have spent another two days just hiking along this contact, looking at this intrusive relations.

We spent our final night in the park enjoying the sounds of a nearby waterfall, nature's white noise machine. Only one more day in Torres del Paine...

Labels: chile, glacial landforms, glaciation, granite, ice, igneous, miocene, national parks, patagonia, south america, travel, weathering, xenoliths

Rested up from Day 1 in Torres del Paine, we were pleased to see that day 2 dawned bright and sunny.

Lily takes a morning break to shed layers:

The weather in Patagonia was really variable, as was the trail. This meant that all day long, we were stopping to put on layers or take off layers as we got cold or hot. It was kind of a pain. Whine whine whine.

All day, clouds scudded along, but we didn't get any rain until late in the day. The main part of the Paine massif was coming into view. Here's a shot from noon-ish:


Here's a shocker: ...We saw more rocks!

Here's another graded bed:


And a little plumose structure, showing a nice twisty hackle fringe:


When I first saw this outcrop, my brain's pattern-recognition center peeped: "CRINOID STEMS!"

...But upon closer examination, they lacked pentameral symmetry, and were some were kind of lumpy. And considering the main rock here is Cretaceous-aged, crinoids could be present, but they aren't as likely a candidate for fossilization as they would have been if these rocks were Paleozoic. So I think these were concretions of some kind. Chert? I shared this image with Patagonia geology expert Brian Romans, and he pointed out something I hadn't noticed in this image: the flame structure in the lower left. That indicates this boulder is upside-down, relative to its original depositional position.

Here's another concentrically-zoned jobbie, which I interpret as a concretion. Overall, this thing was like a pig-in-a-blanket, but on steroids:

I think it's a flint nodule. Brian hasn't seen any crinoids or any concretions in these rocks, so I'm at a loss to offer further explanation.

I was flummoxed by this one, too:

This time, the pattern-recognition center wanted it to be a trilobite, but that's impossible (or, strictly speaking, not impossible but history-re-writing-able) in these aged rocks. Brian tells me it's almost certainly an inoceramid bivalve. That works for me.
(...Or could it be... pseudosegments???)

We walked on, through fields of little white flowers:


Angling towards the main massif, more gnarly peaks came into view...


One thing you can see well in this shot is the contrast between the color of the darker Cretaceous-aged sedimentary host rocks (turbidites) and the light-pink-colored granite which intruded them around 12 million years ago (Miocene).


A bit further on, we could get a decent look at the intrusive relations (through binoculars):

(In this annotated photo, "T" is for "turbidite," "Gr" is for "granite.")

We dropped down off a moraine towards Refugio Dickson, where we made tea, rested a bit, and pushed on again...


At the head of Lago Dickson was an impressive looking glacier, dropped down out of the South Patagonian Ice Field and into the lake:


It was around 1pm when we got to Dickson. We were tired, but the day was only half over. We decided to push on, and essentially do two days' hiking in one. Next stop: Refugio Los Perros!

We hiked on through PRIME Magellanic woodpecker habitat, and it just KILLS me that I didn't see one there, though I did see a few other new birds. Then the rain started, and we started to get tired. But we were committed at this point... We pushed on, and on, and on, and on, climbing up through a forested valley, until finally we popped out on fresh glacial moraine, and saw this:

That's the Los Perros Glacier! A short distance further up the valley was the campground. At this point, the rain had morphed into snow, blasting us in the face as we slogged along, really looking forward to dinner and sleep. Maybe not in that precise order. Eventually, we got there.

Fortunately, the clouds parted for literally 5 minutes, and we were able to have our portrait taken by a doctor from Santiago, who was hiking there for Christmas with his family. They were literally the only Chileans we met who were in the park as tourists (i.e., not park employees or concessionaires) our entire trip. I think we look happy to be in such a special place, don't you?


Next up: Day 3, when we cross John Gardner Pass and see the Grey Glacier for the first time!

Labels: chile, cretaceous, fossils, glaciation, granite, miocene, mountains, patagonia, primary structures, sediment, structure, travel

PALEONTOLOGICAL SOCIETY OF WASHINGTON

Maryland in the Miocene: Paleoenvironmental History of the Calvert Cliffs
Susan Kidwell, Williams Rainey Harper Professor of Geology
Department of Geophysical Sciences, University of Chicago

Wednesday, Sept. 16, 2009
7:00 p.m., in the Cooper Room, National Museum of Natural History (10th St. and Constitution Ave. in NW Washington, DC)

Meet in the Constitution Avenue lobby at 5:00 p.m. if you wish to join the PSW members for dinner at the "Elephant and Castle," NW corner of 12th & Penna. Ave., NW

Non-Smithsonian visitors will be escorted to the Cooper Room at 6:30 and 6:55 p.m.

Labels: dc, fossils, maryland, meetings, miocene, psw, smithsonian

And now, a few images from April's Environmental Geology class field trip. We made three stops: (1) a large coal-fired power plant in Maryland, (2) Westmoreland State Park in Virginia to look at coastal erosion, and (3) Prince William Forest Park in Virginia to look at pyrite emplacement and acid mine drainage.

Here's one of the bluffs on the Potomac River at Westmoreland:

Note the recent pile of breakdown in the middle of the bluff where all the water seepage is, and also the orange trail as soil from the uppermost bluff has marked another mass wasting event's passage down to the river.

These are Miocene-aged sedimentary layers known as the Calvert Formation, part of the Coastal Plain. In places, the gray clay has been altered along fracture surfaces, as shown by these orange stripes criss-crossing one another. My toes for scale:


The students spent some time searching for fossils: this is an area where lots of shark teeth are found. We didn't have much luck, but after a long cold winter, it was nice to be standing in the warm sunshine and water:


At Prince William Forest Park, we hiked down to the Cabin Branch Pyrite Mine to look at the massive denudation there due to acid mine drainage, and we also spent some time poking around for treasures, in this case chunks of pyrite:


We had better luck than at Westmoreland...




...But of course we were in a national park at Prince William, so we left the pyrite where we found it. (Westmoreland, in contrast, allows you to keep any fossils you find in loose sediment: that figures, eh?)

I'd like to say that the group of students I had in Environmental Geology this past semester was terrific, one of the best groups I've worked with in a long time. Maybe it was because the class was discussion-focused, or maybe it was the cookies we ate every Tuesday night, but it was a great experience for me, and I'm looking forward to teaching the course again. Thanks, everyone, for making it so much fun!

Labels: coastal plain, environmental, field trips, maryland, miocene, nova, ore, piedmont, virginia