Rocky Mountain Section - 72nd Annual Meeting - 2020

Paper No. 4-1
Presentation Time: 8:30 AM-4:30 PM


GRASSO, Kyla, Department of Geosciences, Idaho State University, 921 South 8th Ave, Stop 8072, Pocatello, ID 83209 and THACKRAY, Glenn D., Department of Geosciences, Idaho State University, Campus Box 8072, Pocatello, ID 83209

Landscape disturbance events (e.g., earthquakes, landslides, floods) play key roles in landscape evolution in tectonically active areas. Similarly, glacial and alluvial processes alter landscape geomorphology along mountain range fronts, introducing landscape complexity. Along the 70-km Teton range front, fault scarps are well-expressed geomorphically and vary in height by up to tens of meters over short (<1 km) distances. Variable fault scarp height may be explained by 1) along-strike, variable offset rates of the Teton fault; 2) variable erosion of the fault scarp by Pleistocene glacial processes; 3) variable ages of landforms; 4) erosion and deposition by mass wasting and alluvial processes that have occurred since deglaciation; or 5) some combination of these factors, and possibly others.

LiDAR-based mapping of the fault zone indicates that scarp height is affected by glacial geomorphology, mass wasting, and alluvial processes. At a broad scale, vertical separation across scarps increases in the central portion of the fault. At a finer scale, vertical separation of scarps is lower in the floors of deglaciated valleys than on neighboring glacial moraines (e.g., Phelps Lake), reflecting both valley floor processes and younger landform ages. Anomalously high scarps (>15 m vertical separation) are likely an artifact of greater landform age. Landslides influence vertical separation by erosion and burial. Scarps that cut alluvial landforms are typically lower and more diffuse other Teton fault scarps.

The vertical offset of normal fault scarps is expected to systematically increase in the central portion of the fault. However, overall vertical offset of Teton fault scarps increases toward the south. Typical vertical offset is ~12 m from the north end of the fault to the south end of Jackson Lake, ~16 m from Jackson Lake to the south end of Jenny Lake, ~11 m from the south end of Jenny Lake to Granite Canyon. Within the first two of these areas, vertical offsets decrease toward the ends of each. South of Granite Canyon, the fault bifurcates into two strands with typical vertical offset of ~28 m. These anomalously high scarps may be the result of greater landform age or variable offset rates. The transition zones between these four areas may represent boundaries between fault sections or segments.