Sand appears to be forming in the moss along the shore ( A) a blue fiber sticks out of the grain B) this organic structure runs upward through all three of these grains C) moss leaves are trapped inside the
grain).
Mendenhall Glacier Sand Is Not Ground-up Bedrock.
This page is intended to share my 10,000 photos of more than 800 samples from Alaska, Tasmania, Maine and Oregon. I also have samples in my storage unit that I can send you. I need to find a place for all this material. Thanks. Email me.
Please scroll down the page for more photos and discussion….
Summary and Gallery
Below: The large grain is about 1mm and was collected with a magnet. The dark blue materials are presumed to be magnetite. 1950 is the C14 radiocarbon date of the organic material.
The silica surface is smooth and shiny, but uneven, showing many little opalescent patches that look like pores (A) notice how the organic material goes into, and out of, the grain. Inside it is silica, outside it is organic. B) This is a magnetic particle so this darker bluish material must be the magnetite. However, it doesn’t look like either massive or crystalline magnetite and it does have lots of stems and other organic structures running through it. C) This is a moss leaf. D) A small tubular structure projects from the surface, but it is organic at the tip. There is no way anything this fine survived a glacial rock tumbler.
The “ground up bedrock” theory would suggest this grain was broken from the bedrock in a fractured state. Travel under the glacier would have smoothed the surface… then some time later the moss and roots would have to invade the grain. In this case they would have done that since 1950. How they would grow through a sand grain in such diversity and abundance is a great mystery.
Then after somehow getting inside, the organic material would have to be replaced by minerals. It’s a really complicated story compared to the one where the organic material is there first and the minerals are deposited in them later.
Abstract
Sand at Mendenhall Lake is reported to be glacial moraine (Miller, 1957), bedrock ground-up by the glacier and dropped on the shore before the glacier melted back in the 1940’s. This “ground up rock” idea is a theory: there is no way to confirm it by direct observation.
Direct observation does not support the theory.
Photos of Mendenhall Lake sand and gravel document the formation of sand grains composed of silicates and magnetite in moss and peat along the shore. Radiocarbon dating indicates sand on the surface of the beach likely formed since 1950. The grains are all connected together and have molded, not fractured, surfaces. Adjacent grains conform to each other except where spaces between grains are filled with a dark silicate matrix. Organic fibers and the silicified remains of organic fibers also connect adjacent grains. Silica and magnetite sand appears to be forming at all levels in “lanky moss” and the peaty sand beneath it. Lanky moss at Eagle River Beach, about 40 kilometers away on the coast shows similar sand formation. It appears therefore that the glacial location is not as important as the community of organisms that live in the moss.
Gallery
The grain has a molded surface as shown by the notch on the lower left.
In Photoshop the image of the tip of the leaf just to the right of the grain was copied and pasted into the notch… it’s a perfect fit, a molded surface and the grain formed in moss.
The arrows indicate where strands of fungus from either side of the moss leaf enter the grain of silica. The fungus “transits”... Read more....
Silica is replacing fungus: This root with attached moss, peat and sand was photographed in bright sunlight. Then to show the deposited silica, a digital photo processing program, Photoshop,
was used to reduce the brightness and isolate the brightest parts of the image. These brightest spots also show a rainbow play of all colors suggesting the silica is likely opal.
Fungus in “Interglacial wood” (2-3,000 year old wood covered by the most recent advance of Mendenhall Glacier) on he shore of Mendenhall Lake also is being replaced by silica. Below is a
photo of this wood taken in bright sunlight with the brightness decreased to reveal the colorful silica, the brightest parts of the image.
Similar sand and gravel deposits are found in Tasmania,... Read more....
This is sand from the mouth of Eagle River:
The grains were supposedly formed as glaciers ground the bedrock into fragments of sand gravel and silt. They were then carried down the valley in a big glacial rock polisher where the sand was ground finer and gravel and cobbles were rounded. Finally, the sand and gravel were tumbled downstream by the river and deposited at the mouth where... Read more....
Lanky moss, Rhytideadelphus loreus, is a community of organisms, a moss forest with a vertical structure:
- Upper growing moss with green leaves
- Lower brown stem, attached sand grains with organic material, fungus, moss rhizomes, rhizomorphs, mychoryzae incorporated in the grains, all of which conform to each other in such a way they must have formed in place.
- Peat... Read more....
The organic material either grew into these grains or the grains formed around the organic material. Adjacent grains fit together and overlap each other.
So what would all that organic material want inside a grain of silica? Are roots or rhizomes known for growing luxuriantly and without any apparent difficulty into crystalline silica? The grain surface conforms to the organic material... Read more....
References
Barnwell, William W., and Boning, Charles W., 1968, Water resources and surficial geology of the Mendenhall Valley, Alaska: United States Geological Survey.
Connor, C. and Daniel O'Haire, 1988. The Roadside Geology of Alaska. Mountain Press Publishing Company, Missoula, Montana.
Drinkwater, J.L, Brew, AB and Ford, A.B., 1995. Geology, Petrology and Geochemistry of Granitic Rocks from the Coast Mountains Complex near Juneau, Southeastern Alaska. USGS Open File Report 95-638. 126 pages
Drum, R. W., 1968. Silicification of Betula wood in vitro. Science, Vol171 No. 3837 (July 12).
Gehrels, G. and H. Berg, 1992. Geologic Map of Southeast Alaska., U.S. Geological Survey, Denver, Colorado.
Krauskopf, K.B., 1959. The Geochemistry of Silica in Sediments. SEMP Silica in Sediments (SP7).
Miller, R.D. 1973. Gastineau channel formation, a composite glaciomarine deposit near Juneau, Alaska. USGS contributions to stratigraphy, U.S. Govt. Printing Office.
Miller, R.D. 1972. Surficial Geology of the Juneau Urban Area and Vicinity, Alaska. Open- file report U. S. Geological Survey (map and booklet).
Motyka, R.J., O'Neel, S., Connor, C.L., and Echelmeyer., 2002. 20th Century Thinning of Mendenhall Glacier, Alaska, and its Relationship to Climate, Lake–Calving, and Glacier Run–Off. Journal of Global and Planetary Change. V. 35, pp. 93–112.
USDA Forest Service Region 10, 2013. Mushrooms of the National Forests in Alaska, PDF.