[Journal entry for May 30 – June 3, 2013, Summer Intern Workshop and Fieldtrip]. Five LDEO Summer Interns, Philip, Maggie, Matt, Rose, Sarah participated in this Workshop and Fieldtrip. The morning workshops, which focused on continental evolution, were held in Cabin F at Baker Camp (Harriman State Park). The afternoon fieldtrips focused on the history of deformation in the Proterozoic rocks of the Hudson Highlands, within and adjacent to the Park.

May 30, 2013. We met in front of the Geoscience Building at LDEO and drove up to Baker Camp in one of the Department’s vans. As there were only six of us, we were able to remove the back seat of the van to free up space for luggage, and still have comfortable seating. The drive up to Baker Camp took about a half hour. As we drove up to the Camp, we noticed the tailings of an old mine, visible from its access road.

Baker Camp is a collection of cabins and lodges on the northeastern shore of Lake Sebago, in Harriman State Park. It was built in the 1920’s by George Fisher Baker, a financier from Tuxedo NY, to benefit his workers. It is now owned by the Park but is privately operated. I had met the proprietor, Rae Hirsch, back when I was a volunteer kayak coach at the neighboring American Canoe Association camp. She is a pleasant and straightforward person, easy to do business with. She and I chatted about the damage wrought by Hurricane Sandy, which felled many trees in the Camp, several of which damaged cabins. Rae assigned us to Cabin F, located at the northeast corner of the camp, on a hillside high above Lake Sebago.

We unpacked and organized ourselves. I set up our two Coleman stoves on a rock ledge adjacent to the Cabin – these stoves cannot be used indoors on account of the carbon-monoxide hazard, and would make the cabin too hot, anyway. The interns made the salad while I cooked chicken parmesan. We then sat on the deck of the cabin and had a relaxing dinner.

After dinner, the interns and I set up our seismometer, on a rock ledge adjacent to the cabin. I had brought it along as part of a data-collection demo; it included a RefTek 130 recorder and a Mark Products L22-D geophone, along with battery and GPS antenna. As always, the “stomp test”, where one kicks the rock and observes the resulting wiggles on a computer screen, generated some smiles. The interns then spent an hour doing their “homework”, preparing simple demos and reading short papers that we would discuss the next morning. While they were reading, I walked down to the lake shore and relaxed. I spotted a deer wandering around the camp as I strolled back to the cabin.

May 31, 2013. We were treated to a beautiful sunny day. I arose at about 7AM and made hot water for coffee on the stove. We then had a breakfast of bagels on the deck of the cabin. A deer walked by as we were eating.

We then began our morning workshop, which lasted for about ninety minutes. I gave a short overview, explaining how it came to be that we were focusing on continental evolution, the goals and procedures of the four sessions, and the setting in the Hudson Highlands. The interns then presented three physical-model based demos that illustrated three important geological processes, differential erosion (Rose, using a sandbox), isotasy and (Matt and Philip, using floating boards) and uranium-lead decay (Maggie and Sarah, using coins). We then discussed two short papers:

Boyd, Gurney & Richardson, Evidence for a 150-200-km thick Archean lithosphere from diamond inclusion thermobarometry, Nature 1985.

Zegers & van Keken, Middle Archean continent formation by crustal delamination, Geology, 2001.

We concentrated on identifying the hypothesis being put forth by the author, the type and quality of the data presented, and whether the analysis credibly tested the hypothesis. We used a white board to make simple sketches of the processes and to help us to understand the figures.

We then packed up a lunch and began the fieldtrip, which was a traverse across the region. I gave my standard lecture on field safety (the importance of sunscreen and hydration; avoiding dangers including traffic, poison ivy and ticks; what to do if someone became separated from the group) and a tutorial on taking field notes. I always log the date and time of each stop, its location (including road names and GPS coordinates), and a physical description of the site, as well as any observations or measurements made there. One of the interns was assigned to operate a pocket GPS receiver and to announce them to the rest of us. I also handed out compasses and showed how to use them to measure the strike and dip of an interface. I posed as a first hypothesis that the topography in the area was due to differential erosion and charged the interns to collect observations over the next several field stops that would test it.

Stop 1A. Glacially-plucked cliff-face at Baker Camp, Harriman State Park, NY. The Proterozoic gneiss that outcrops here is pretty ubiquitous throughout the Hudson Highlands. We examined its texture and measured the strike and dip of its foliation.

Stop 1B. Stream gulley at Monsey Glen County Park, Money NY. We examined the pebble-rich sandstone that outcrops along the stream. The rock is soft enough that sand grains can be rubbed off with the fingertips. An especially pebble-rich bed erodes easily, making small caves in the hillside. We measured the strike and dip of the beds, noting that they were plunging down towards the Highlands. I posed the hypothesis that the source of the sediment was the Highlands and we came up with two tests, that the pebbles should be more common and larger at a site near the mountains and that they should be made of the gneiss that we saw at Baker Camp.

Stop 1C. Rock outcrops along Route 202 – Old Route 202 intersection in Montebello NY. Very coarse conglomerates are exposed here, packed with clasts that can be as large as a football. However, the clasts are obviously not composed of gneiss, but rather of sedimentary rocks, including limestones. We discussed our hypothesis in the context of these new observations and decided that we should take a closer look at the nearby hills to see what kind of rock they were actually composed of.

Stop 1D. Overlook at Kakiat County Park, Montebello NY. We parked near the bathroom building, crossed the Mahwah River via a footbridge and took the Mountain Trail (blazed in orange) up to an overlook that’s about two-thirds of the way up Cobus Mountain. The Seventeen Year Cicadas (this is one of their swarm years) were humming in the canopy above, and some of their “shells” were still clinging to tree trunks. The rock here is hornblende granite, not gneiss, though it has been metamorphosed a little. We measured the orientation of the foliation. We could see on the topographic map that this area was somewhat higher than the region with the gneiss, and hypothesized that this elevation difference, too, was due to differential erosion. We also talked about the boundary between the sediments and the gneiss of the Highlands, noting that the sediments dipped in the wrong direction for them to lie conformably on the flanks of the metamorphic rocks. We hypothesized that there was a normal fault and discussed what kind of observations would test it.

We had lunch at the overlook, relaxing in the shade under a tree, and gazing out into the Newark Basin. A few turkey vultures circled about. The day was sunny and rather hot. The sky was a little too hazy to make out the Manhattan skyline, which on a clear day can be seen on the southern horizon.

Stop 1D. Road cut at Pavilion Road, Suffern NY. We were lucky to have access to this outcrop, for a sign said that the roadbed is about to be repaved. The cliff face here has polished surfaces with dramatic near-vertical slickenslides, indicative of a dip-slip fault. We spent a few minutes looking for features that would verify that the motion was normal, as contrasted to reverse, but found nothing convincing.

Stop 1E. Bear Mountain, NY. We drove to the summit of Bear Mountain, both for its excellent view and to verify that this high point is also composed of granite. From this vantage, we could see the crest of the ridge that extends southwestward towards our previous stop in Kakiat Park, twenty kilometers or so away. We measured the foliation here; it has a different direction than at Kakiat. Sarah argued that the rock is really low-grade gneiss and not granite, per se. She is, of course, completely correct. However, in Precambrian terrains almost everything is metamorphosed to one degree or another.

We discusses the relationship between the granites and the gneisses; the age relationships between gneiss, granite and deformation. We outlined several hypotheses consistent with the little that we know already. I urged that we consider what kinds of observations might be made on tomorrow’s fieldtrip that would discriminate between the hypotheses.

We the returned to Baker Camp. The interns took a brief swim in Lake Sebago, while I relaxed in the cabin. They then cooked dinner, a vegetable curry served over rice. After cleaning up from dinner, I took a brief swim in the lake, too.

We devoted an hour of the evening to “homework”. I gave a brief presentation of the use of seismic tomography to infer lithospheric temperature, using images taken from:

Van der Lee & Nolet, Upper-mantle S-velocity structure of North America, Journal of Geophysical Research, 1997.

as this data type played an important role in one of the papers that I had assigned. We spent the rest relaxing and chatting

June 1, 2013. It’s another beautiful sunny day. I arose at about 7AM and made breakfast; pancakes served with apple sauce and maple syrup and washed down with coffee. We watched a hedgehog browse in a patch of grass near the cabin.

Dallas Abbott from LDEO joined our morning workshop. We began with two demos: global hypsometery (Matt and Rose) and proxies (Sarah). We put off a third demo on thermal subsidence due to equipment problems. Dallas led a discussion on models of the formation of the continental lithosphere. Finally, we discussed two short papers:

Bowring, Williams & Compston, 3.96 Ga gneisses from the Slave province, Northwest Territories, Canada, Geology 2013.

Eaton & Fredericksen, Seismic evidence for convection-motion of the North American plate, Nature 2007.

The first is describes the current candidate for the earth’s oldest rock. The second is a more speculative paper on using the trace of the New England hotspot to detect lithospheric deformation. We then packed up a lunch and began the fieldtrip.

Stop 2A. Road cut at Seven Lakes Drive near Lake Sebago Dam, Harriman State Park NY. The gneiss here contains both graphite and pyrite, which together are evidence that the protolith was an organic-rich sedimentary rock. We measured the strike and dip if the foliation, found several layers rich in garnet, and examined a small-offset fault.

Stop 2B. Road cut on Route 106, just east of the Long Path crossing. We parked at Lake Skannatati and hiked the Long Path (blazed in blue), past Lake Ascoti and through the woods about a half mile east to Route 106. A nappe fold with a basal shear zone is exposed in the road cut. We discussed the sense of motion needed to produce such a structure.

We then returned to Lake Skannatati. Pumpkinseed Sunfish (“sunnies”) have made numerous nests in the shallows of the two lakes. We ate lunch as we watched flotilla of Canada Geese paddle across the lake. We also spotted a Northern Water Snake, partially-submerged beneath the surface.

Stop 2C. Road cut on Route 106 just west of Lake Kanawauke. We parked at the Lake Kanawauke picnic area, paying a parking fee of six dollars. We then walked westward on Route 106, along the south shore of lake. Blatterwort, an aquatic plant with yellow blossoms on tall stalks, are blooming in the lake. The delta on the north side of the lake, formed two years ago during Tropial Storm Lee, is still unvegetated and brightly visible.

I had the interns make sketches of this outcrop, which features pegmatite dikes cutting gneiss. We noted that the gneiss has a well-developed banding and that the dikes are undeformed.

Stop 2D. Ledge by Little Long Pond. We continued westward along Route 106 a few hundred meters and then walked out onto a small peninsula that extends south into Little Long Pond. I had the interns sketch a section of the ledge here which features a dike cutting a pod of grey-colored gneiss. Both are very deformed, evidence that some kind of very-localized zone of intense deformation cuts across this region. This is a second phase of deformation created by a shear zone, the weathering of which formed the valley in which a series of lakes – Sebago, Kanawauke, Skannatati - now sit.

Stop 2E. Road cut along Seven Lakes Drive beween Cedar Pond Group Camp and the Park Camp Office. We parked at the Lake Tiorati picnic area, paying an extra two dollars to upgrade out parking permit for this lot. We then walked south on Seven Lakes Drive to a point just north of the Cedar Pond Group Camp, where a diorite pluton is exposed in the road cut. The pluton clearly cuts the gneiss, and a zone of contact metamorphism about ten centimeters thick has developed on the boundary. This pluton adds another event to our list; we discussed what evidence that might enable us to establish relative timing.

We the returned to Baker Camp. While the interns swam in Lake Sebago, I rented a kayak and paddled on Lake Sebago. Wayne, one of the Baker Camp staff members, helped me prep the boat. I had brought my wing paddle, and so was able to paddle the short recreational kayak at a fairly good pace. I first paddled up to Sebago Beach, where I was rather appalled to see how much grass has grown on the beach sand. The Park does not seem to be preparing to open this beach this year at all! I then paddle the eastern arm of the lake to the Pump House.

Rose and Philip cooked us a dinner of fried chicken, corn on the cob and garlic bread. A wild turkey wandered by as the rest of us relaxed. Once again, we devoted an hour to “homework” and then spent the rest of the evening relaxing. I prepared a demo, cutting up one of our North American geological maps into sort of a jigsaw puzzle that I could use to re-enact its geological history.

June 2, 2013. We are treated to another beautiful sunny day. I arose at about 7AM and made breakfast; croissants and cheese omelets, together with coffee. We watched a group of four or five deer, including a buck with sprouting antlers, wander past the cabin. They all looked rather skinny and one of the smaller ones has an injury on its flank. I suppose that they had a hard winter.

I began our morning workshop with my North American history demo. It emphasizes how little is known about pre-Grenville Orogeny events. We then discussed two papers:

Calvert, Sawyer, Davis & Ludden, Archaean subduction inferred from seismic images of a mantle suture in the Superior Province, Nature 1995

Spray, Kelley & Rowley, Evidence for a late Triassic multiple impact event on Earth, Nature, 1998.

The former provides important evidence for Archean plate tectonics. The latter is much more speculative but (perhaps for that reason) rather thought provoking and fun.

We then packed up a lunch and began the fieldtrip.

Stop 3A. Road cut along East Village Road in Tuxedo NY. We parked at the Ramapo River boat launch off of East Village Road and walked the road towards the Thruway underpass. We passed an outcrop of gneiss that displays a very nice fold.

Stop 3B. Gneiss outcrops along the Tuxedo – Mount Ivy Trail. After walking beneath the Thruway, we headed north on Grove Dr. to the Tuxedo – Mount Ivy (TMI) Trailhead. We then hiked this trail (blazed in red), steeply uphill through the woods. We stopped at a large outcrop and measures the foliation direction of the gneiss.

Sarah found a magnetite pebble along the trail, which we tested with a magnet that I had brought with me. It is very magnetic. Many of the trails and woods roads in the Park follow Revolutionary Era iron mines and were paved with waste from the mines.

Stop 3C. Glacially-plucked cliff at Claudius Smith Den. My hiking map says that Claudius Smith was a notorious Revolutionary Era outlaw who stole from the Continental Army and who was eventually captured and hanged in 1779. His band used a small cave on this glacially-plucked cliff as a refuge. I had the interns spend about fifteen minutes hiking around the base of the cliff looking at the rock types. There are two: the gneiss that we had been seeing along the trail and which forms the rock ledges below the level of the cliff, and granite broadly similar in character to the one that we had seen previously at Kakiat Park and Bear Mountain, which forms the cliff face. A clear cross-cutting of the gneiss by the granite is evident in several places, and especially along TMI as it ascends to the top of the cliff.

We had lunch at the top of the cliff, admiring the beautiful view of the Highlands to our west. We discusses the significance of the granite being younger than the gneiss, yet both having identical foliation. We also examine the surface of the granite ledge, which has a undulating topography, developing several hypotheses about its origin (fold in the granite, glacial furrows, casts of folds in an overlying gneiss). We hiked up to a higher ledge that turned out to be gneiss, indicating that the granite layer a few tens of meters thick. We then headed the back to Tuxedo.

Partway down TMI, we passed and gave directions to a group of hikers who had wanted to go to Lake Sebago, which is about two hours east on TMI from the Den, but who seemed to have become disoriented and were heading west from it. The trails and woods roads of Harriman State Park are notoriously windy and tricky. Without a compass and map you can really easy wind up losing your way –often without realizing it – and wind up someplace you never intended!

We stopped at Bentley’s Deli in Tudedo NY for Ice Cream.

Stop 3D. Mine near Baker Camp. I had initially planned to visit the Boston Mine, near the intersection of Island Pond Road and the Dunning Trail. However, the closest parking, on Route 106 where it intersects Island Pond Road, was inaccessible due to construction on Route 106. I therefore took the interns to the mine near Baker Camp. This proved a happy choice, for that mine turned out to be similar to the Boston, and much less of a walk.

The mine is along the Baker Camp access road, about a kilometer east of the Camp, just west of the intersection with a woods road. The waste pile, a meter-high, flat-topped pile of angular stones is easily recognizable from the road. Many of these stones have magnetite concentrations high enough for the magnet to adhere. The mine itself is a small slot in the hillside. A magnetite vein, about half a meter wide, is exposed on the back end of the slot. Very little, if any ore seems to have been removed from the site. Paul Olsen, who visited the site the next day, speculated to me that it was only made to assay the ore, not to commercially mine it.

Back at Baker Camp, the interns prepared a dinner of salad, macaroni and cheese and garlic bread. Clouds had developed during the night and a little rain began to fall. After dinner, I gathered a small pile of kindling in order to make a short-lived fire in the cabin’s fireplace, so we could roast marshmallows. After this treat, we spent an hour on “homework” and then relaxed for the rest of the evening. I walked down to the lake shore late in the evening, and watched lighting in thunderheads to our south.

June 3, 2013. Heavy rain fell during the night, but was tapering off by morning. I arose at about 7AM and moved the stoves to an overhang beneath the cabin. I then cooked up a large batch of blueberry pancakes.

Paul Olden from LDEO and Masa, a postdoc, joined our morning workshop. Paul gave a presentation on the Central Atlantic Magmatic Province (CAMP), a continental flood basalt event that includes the mafic rocks of the nearby Hudson Palisades Cliffs. We had read several papers in preparation:

Self, Thordarson & Widdowson, Gas fuxes from flood basalt eruptions, Elemengts 2005.

Olsen, Giant lava flows, mass extinctions and mantle plumes, Science 1999.

Schaller, Wright & Kent, Atmospheric PCO₂ perturbations associated with the Central Atlantic Magmatic Province, Science 2011.

One of the fascinating aspects of CAMP studies is the “blind man and the elephant effect”: individual lavas from Europe, Africa and the Americas were studied for many years by different people without anyone realizing that they were all related. Paul’s presentation covered the geodynamical aspects of the CAMP, the possibility that it caused the Triassic-Jurassic extinction and its potential use as a place to sequester anthropogenic CO₂.

Paul and Masa joined us for today’s fieldtrip, which had only one stop:

Stop 4A. High Tor. I had hoped to park at High Tor State Park, along South Mountain Road in New City NY, but it was closed. Instead, we parked at the top of South Central Highway, in Mt Ivy NY, and took a considerably longer route, following the Long Path (blazed in blue) eastward along the crest of the Hudson Palisades Cliffs. We passed several rock ledges with clear glacial scratches, as well as copious glacial erratic boulders, most of Hudson Highland gneiss, but a few of Newark Basin sandstone, too. The trail is relatively flat, except for the final section that ascends High Tor, itself. Last night’s rain had completely ended, and the day was now hot and sunny, with puffy clouds.

High Tor (tor being derived from the Dutch word toren, meaning tower) is a rocky high point on the Hudson Palisades Cliffs, about where that hogback ridge makes its turn from a north-south orientation that follows the Hudson River to and east-west orientation that cuts inland. The eye can follow the ridge line of the Palisades from Suffern in the west, all the way south to the Manhattan skyline. The view of the Hudson Highlands is also excellent. The eastward jog of the Hudson River, as it follows the Ramapo fault, is clearly visible. The ledges on the top of High Tor are the best place of which I’m aware to see the tops of the rock columns that, when viewed from the side, are reminiscent of the wooden palisade around an old frontier fort (from whence came the name).

We had lunch in a shady spot atop High Tor. We then walked back, and after a stop at the Courtesy Mart in Mt Ivy for Ice Cream.

I dropped the interns off in front of the Geoscience Building at LDEO. Philip stayed and helped me unload the van, gas it up, vacuum it, and re-install the back seat.

A couple of hours shy of four days.

Acknowledgement. Several of the fieldtrip localities were drawn from Gates, Valentino, Gorring, Chiarenzelli & Hamilton, Field Trip to the Western Hudson Highlands, New York