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|Title:||Geophysical investigations of an anomalous unfrozen zone, Caribou Peak, Alaska|
|Authors:||Lawson, Daniel E.|
Arcone, Steven A.
Collins, Charles M.
|Publisher:||Cold Regions Research and Engineering Laboratory (U.S.)|
Engineer Research and Development Center (U.S.)
|Series/Report no.:||CRREL report ; 91-17.|
Abstract: The occurrence of unfrozen materials and groundwater flow on a north-facing slope in interior Alaska is important to recognize, both for predicting the spatial distribution of perennially frozen ground as well as for understanding watershed hydrology. An anomalous unfrozen zone or talik was located on the northern slope of Caribou Peak by drilling in April 1985. Impulse radar surveying of the area immediately adjacent to this drill hole, as well as on three transects upslope of its location, revealed that the unfrozen zone is the result of groundwater flow in the bedrock along a relatively planar zone, interpreted as a fracture. This fracture and two others located by the radar are continuous in the direction of the slope, trending generally N20°E and dipping about 9° east. Geologic logs indicate that the drill hole intersected a fracture in the bedrock, a quartz—muscovite schist, at a depth of about 8.5 to 9.0 m. Downhole measurements show ground temperatures at this depth are generally uniform and slightly above freezing throughout the year, suggesting continuous flow of groundwater within the planar structure. Analysis of the freezing point of the groundwater sample indicates normal freezing beginning at 0°C, while ion chromatography indicated that the water was fresh and not highly mineralized. Vegetation patterns, coupled with the borehole location and fracture orientation, suggest that flow originates within the upper and central parts of the peak and discharges into the valley of Poker Creek. The source of the groundwater is unknown, but appears to be an aquifer in the south-facing, non-permafrost side of Caribou Peak that is intersected by the north—south striking fractures. These fractures then transmit the water to the northern face and channel it through the permanently frozen layer beneath this side. In addition to identifying these unfrozen, localized groundwater flows within perennially frozen bedrock, the radar profiles also revealed signatures that suggest a transition in unfrozen water content within the marginally frozen colluvium.
|Rights:||Approved for public release; distribution is unlimited.|
|Appears in Collections:||CRREL Report|
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|CRREL-91-17.pdf||1.67 MB||Adobe PDF|