Sunday, July 12, 2009

7-10-09 Researching Soil Development and Plant Succession at the Site of a Landslide on the Gale River Trail.

Morning sunlight on the Gale River at first crossing... I've mentioned this particular place before in the blog as one that has a lot of meaning to me. It represents the beauty of these woods and rivers and evokes a sense of enchantment and timelessness. The light and the river and the trees all conspire to make me feel 17 years old again (which is a good thing). Anyway, I hopped across the Gale here on Friday (7-10-09) on my way to the research site where I want to look at soil development following an "event" that might provide a facsimile of soil development that might have occurred thousands of years ago here when the last continental glacier passed right by 1st crossing as it advanced southward towards Cape Cod. It tore up trees and plants and plowed off the top soil as it advanced, then deposited a lot of "till' in the form of gravel, sand, rocks and boulders, and possibly other material made up of organic matter including, maybe, a lot of different seed stocks as it retreated and melted.

The site I picked is where a landslide came down off Mt. Garfield and slid into the Gale River tearing up trees and clearing off the topsoil and leaving a lot of debris in a process similar to a glacier advancing and then retreating only much faster. The slide came down either during Hurricane Carol on August 31, 1954 or Hurricane Diane on August 20, 1955. I'm picking Diane because that storm lashed the White Mountains with record breaking rain. Hurricane Carol was destructive but did not produce the heavy rainfall that Diane did. It doesn't make a lot of difference, actually. The point is that the slide occurred roughly 55 years ago.

The leaf canopy above the Gale River is vibrant and healthy and shimmering with light.

The Gale River Trail threads beside the river for several miles. It follows an old logging road once used in the winter by horse teams pulling heavy sleds of logs that were cut on the steep mountain slopes in the early years of the 20th Century. Some logging was also done here in the 1950s and 1960s. (And there's some logging going on now but on a much smaller scale.)

At 2.7 miles from the parking lot the trail reaches these steps which designates the slide where I'm doing the research. The steps are a measurement of how much debris the slide left behind when it came down. It's almost 20 feet thick. The slide came down across the flood plain of the river and then across the river itself making a dam. The slide was moving west to east and came down in mid morning. By early afternoon a small lake had formed on the upriver side of the dam. The dam burst sending a wall of water down the valley. The surge caught one of the Galehead croo as he was packing back up after meeting the truck and he had to drop his packboard and scamper up a nearby a tree to avoid being swept downstream. He never found his packboard.

This is what the site of the slide looked like in November 1967, 12 years after the slide. I wish I had taken more pictures with more detail when I took this one because this is only half of the debris left by the slide but the photo still contains a lot of useful data.

This rock will help us get oriented.

It's the same rock I photographed back on 2-14-09.

The rock in the photos above is #1 in the photo.

These rocks are #2 in the photo above. The #1 boulder is in the background. So all of the numbered rocks are on the downhill (north) edge of the slide.

The debris left by the landslide is similar to glacial till with a mixture of large and small rocks, sand and gravel. It contains little organic matter.

This is sampling site #1. For a sampling method I measured the overall sampling area which is represented by the slide as it now "sits" on the flood plain of the river. It measures just under 300 feet by 100 feet, or about the size of an American football field. I then used a set of transects, or "lines", to randomly select soil "sampling points" (locations) within that 300 x 100 foot area and I map "plotted" them as 25 x 25 foot squares each and then using one transect I selected five "sampling points" in each of those squares. That gives me at least three, averaged, samples from the site. This was all rather difficult because of the thickness of the growth in some areas. It was like bushwacking up West Bond from the north and my forearms and face were dripping with blood from myriad scratches that I didn't notice until later when I was hiking out.

The black line shows the approximate center of site #1 which.

This is sampling site #2 and is out of the area of the 1968 photograph.

This is sampling site 3 and also out of the area of the 1968 photograph but, as you can see, a little more open and easier to work in.

Due to certain restrictions placed by the US Forest Service I won't actually remove soil as part of the sampling so I had to be inventive. I did some pilot samples using this trowel but not to disturb the soil and only to measure the depth of the "new soil" on top of the slide and to pry it back a wee bit so I could see the soil horizons and take pictures. This method seemed to afford enough of a glimpse so that I could measure the soil and the horizons. There are three definite horizons sitting on top of the slide debris. In my pilot samples I found that the soil varies in depth but also in color and texture. There is a lot of "duff" or fresh organic matter, leaves and sticks, in a semi-decomposed state in the top horizon. Under that there is a brownish soil with a lot of decomposed organic material in it.

The thinnest layer of top soil on top of the slide debris was 1.75 inches thick. The thickest was 6 inches. This conforms the the Uglio did at Glacier Bay in Richard Goldthwait's 1966 study on soild development and plant succession at Muir Inlet, Alaska. I also found the vegetation to be consistent with Goldthwait's data. More detailed sampling will have to wait for another time. By the time I got this far the sun was setting.

A few more points of reference. Before I left I walked halfway up the slide track to see what the uphill portion looked like. In the 1960s on several occasions I packed loads up to to Galehead Hut via the slide (just for the fun of it) when it looked like it does in the accompanying black and white photo so I was familiar with how it looked then. It looks quite different now.

Ken Olson, who was Manager of the AMC Huts at the time, walks across the slide path in the early 1970s (1972 or 1973) as he hikes out of Galehead on the Gale River Trail. The above color photo shows the steep gravel bank that's on the right hand side of the black and white photo. There is a stream that runs through that gully that probably has the best water in the White Mountains.

North (left) and South (right) Twin Mountains seen from halfway up the slide track. This is looking slightly down and across the track and shows the density of the vegetation that covers the south or left hand side of the track that in the black and white photo above is almost bare (the half of the slide just behind Ken and a little above his head).

The canopy height of the vegetation on the slide track today is up there. The poplar tree (Populus tremuloides) in right center is 60 feet high but poplars grow quickly. An anomaly exists in the photo where you see the white pine (Pinus strobus) in the left foreground. It's a mystery how the pine tree got there. There are three white pines in the sampling area all of them have "diameters-at-breast-height" (DBH) of 5 inches so they are relatively new pioneers to this site. But the closest white pines to this site are four or five miles away.

Balsam cones are prolific this year and represents the competitive success of balsam that we see throughout the White Mountains that would be an interesting study in itself.

Sheeps laurel (Kalmia angustifolia) on the upper section of the slide track. There was also a lot of fir clubmoss (Lycopodium selago) fanning out on delicate runners across the slope in a net.

Looking up towards the upper half of the slide track.

The sun was setting and I packed up and headed down the trail in this late afternoon light that was lyrical. It shafted through the woods and glades almost parallel to the ground contrasting with the dark shadows of the approaching evening....the wind blew in a whisper and there were the evening songs of the thrushes, the Hermit Thrush and the Robin, in the hardwoods on the lower section of the trail.

The sun created elaborate patterns of shadows on the boulders at 1st Crossing

and across the trail

as it escorted me back to the trailhead and the parking lot. It was a lovely summer day!

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