Frost Heaving and Surface Clast Movement in Turf-banked Terraces, Eastern Glacier National Park, Montana
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Patterned ground consists of rocks, gravel, and soil, both sorted and unsorted, ordered on a landscape in the appearance of geometric shapes ranging from circles, polygons, nets, and stripes. Patterned ground occurs throughout the world in alpine, subarctic, and arctic regions. These places are increasingly threatened, through climate change, natural and human disturbance, and other disturbances in the surrounding environment of the patterned ground. In order to predict future responses and disturbance reactions of fragile periglacial environments such as patterned ground with active cryoturbation, movement rates need to be determined. Limited research concerning patterned ground in northwestern Montana has been published. In eastern Glacier National Park, patterned ground is evident on several alpine tundra sites; however, rates of movement are not known. Four questions were asked in this dissertation: (1) is surface movement occurring at selected study sites; (2) what are the temporal and spatial movements of individual surface clasts and markers; (3) do the surfaces of the study sites change in appearance over time; and (4) what is the rate of heave occurring at the study sites, temporally and spatially?
In eastern Glacier National Park, data were collected from three locations. Sites with microclimate differences were established at each of the three locations to compare and contrast the movement of surface objects over time. One location consisted of needle-ice pans, whereas the other two locations contained relict solifluction treads and risers. Data were collected from 105 markers, 90 nails, and 90 clasts. Observations of marker and clast sorting within turf-banked terraces occurred between 2003 and 2006, whereas observations of vertical heaving, using nails, occurred between 2005 and 2006. Field data and repeat photography techniques were used to measure and observe marker and clast position changes over time. Types of marker movement were classified into four types: lateral, vertical tilt, burial, and overturning. Clasts were classified by: lateral movement, vertical tilt, burial and rotation. Nails were measured in millimeters from the surface to the nail head.
The results of this research confirmed that the surface of needle-ice pans and relict solifluction treads were exhibiting active surface movement. Laterally, clasts moved more than markers at the same sites. Gravel and sediment burial occurred more frequently with markers than clasts. A majority of the sites changed little in surface appearance over time. Miniature sorted circles with fine sediment enclosed by gravel were observed at two sites in 2003 and another site in 2004 but the circles have since been in a state of disorganization. Possible reformation of the miniature sorted circles at one of the sites was observed in 2006. Differential frost heaving, as evidenced by the heaving upwards of nails, is occurring at the 3 locations. Surface wash was determined to be a process operating at one location, whereas the other two locations were dominated by frost-related processes. Processes not eliminated as contributors or instigators of lateral and vertical surface movement were: desiccation cracking, differential frost heaving, primary frost sorting, and convective cells. Future research directions include the excavation of the study sites to determine the depth of movement and the monitoring of the subsurface temperature of the sites. Additionally, future research will include the assessment of changes in rate of surface movement in response to environmental changes.