Amchitka Bioenvironmental Program. Plant Ecology of Amchitka Island. Final Report. Page: 20 of 56
This report is part of the collection entitled: Office of Scientific & Technical Information Technical Reports and was provided to UNT Digital Library by the UNT Libraries Government Documents Department.
Extracted Text
The following text was automatically extracted from the image on this page using optical character recognition software:
12
Peat Depth and Movement, and Soil Drainage
Depth
Six soil-depth grids were taken (probes 5 m apart on lines 10 m apart) with steel
probes to determine the depth of the lithified breccias and lavas. The grids represented
a systelnatic probing of six drainage basins on the eastern one-half of the island [over
Banjo Point and Amchitka formations (Powers et al., 1960)] at elevations of approxi-
mately 70 meters. The grids indicated the deepest soil was not always in the lowland
valley or stream bottoms but was more often at the lower slope transitions. Figure 2
is a graphic representation of the soil depths on a modal profile. The depth profiles are
complicated by a slow slippage or slump of wet peat toward stream bottoms and sea cliffs
where the topography of the bedrock contact promotes downslope movement. The lesser
depths in valleys and stream bottoms suggest that besides compaction and subsidence, a
hydric dissolution of the organic material occurs, and the brownish coloration of many
streams indicates that a considerable amount of organic material may be carried in
solution and suspension even in streams with low gradients.
Movement
In March and April, 1968, surveys by Holmes and Narver, Inc., assisted in estab-
lishing two semipermament, staked transect lines in Ultra Basin. Control points estab-
lished by the present author in March, 1968, were used. Laths were set at 3-meter
intervals along lines 228. 6 and 176.7 meters long. The peat depths in the transect area
varied from 0.3 to 0.6 meters. The control points at each end were tied to the Island
base control net by triangulation. The upper line crosses a terrace-like area with a
slight slope to the northwest while the longer, lower line, nearly parallel but approxi-
mately 38 meters downslope, crosses a steep northwest slope (25 degrees), 61 meters
across, at about midline. The lower line was located to cross this steeper slope where
apparent past movement of the peat has produced peat pressure ridges at a right angle
to the fall line. All the laths were checked and tapped in vertically (in relation to the
horizon) to bedrock in September, 1968.
In July, 1969, the upper line, located on a very gentle slope, showed no signs of
movement. All stakes were checked for stability. On the lower line, 21 stakes were dis-
placed angularly, 6 indicating movement at the peat surface, and 15 indicating move-
ment at or near the peat-bedrock interface. Displacement from the vertical had a mode
of 15 to 20 centimeters. This displacement indicates a fairly substantial movement of
peat during the period.
The observations taken in July 1969 when compared with those of the summer of
1968 indicate that no plant-community shifts have yet occurred as a result of this move-
ment. The authors have retained the survey data supplied by Holmes and Narver, Inc.,
for further observations and the lines are being maintained.
Soil Drainage
The depth of peat and the degree of drainage reflected by the stage of decomposition
of the organic material correlate with the distribution of plant communities in the low-
land tundra-upland tundra topoenvironmental units. Cooperative field work with Everett
Upcoming Pages
Here’s what’s next.
Search Inside
This report can be searched. Note: Results may vary based on the legibility of text within the document.
Tools / Downloads
Get a copy of this page or view the extracted text.
Citing and Sharing
Basic information for referencing this web page. We also provide extended guidance on usage rights, references, copying or embedding.
Reference the current page of this Report.
Amundsen, C. C. Amchitka Bioenvironmental Program. Plant Ecology of Amchitka Island. Final Report., report, January 1, 1972; United States. (https://digital.library.unt.edu/ark:/67531/metadc1033349/m1/20/: accessed April 25, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.