DIFFERENCES IN AVERAGE SLOPE ANGLES AS EVIDENCE OF VARYING UPLIFT RATES IN THE EASTERN ALASKA RANGE

During the late Pliocene, the climate in interior Alaska became much cooler and drier. The reason for this change is often partially attributed to the rising of the Alaska Range to the south. However current data for the timing of the uplift, obtained from the central Alaska Range, near Mt. Denali suggest that uplift started at ~6 Ma, while the major effects of climate change occur closer to 2 Ma. Such a time difference suggests that either the rising Alaska Range was not connected to the change in climate in interior Alaska, or the eastern Alaska Range (Hayes Range, located between the Delta and Nenana River valleys) rose slower/later than the known uplift rates/dates for the Denali area, allowing the continued flow of warm-moist air into Alaska's interior.

Digital Elevation Models of the eastern Alaska Range also point towards differences in uplift rates within the sub-range itself. Slope angles are much greater on the north side of the Denali Fault in the Black Rapids drainage area compared to the Susitna drainage area north of the Denali Fault System. The fact that the large (M 7.9) 2002 Denali Fault System earthquake caused massive landslides off of the Black Rapids Glacier (mostly metamorphic), but not off of the Susitna Glacier (mostly granitic) implies that the rock types between the two glacial systems differ with the rock being more subject to mass collapse off of the Black Rapids Glacier.

Since the angle of slope is greater in an area that contains rock types that are more erodable, there must either be a difference in erosional forcing rates between the Susitna and the Black Rapids drainages or a difference in uplift rates. Precipitation rates are relatively constant between the two systems, implying similar erosional forcing rates. Different uplift rates across the range can be related to relative position along the Denali Fault System, isostatic response, different rates of plate motion (Yakutat Block and Pacific Plate) forcing, or a combination of two or three of these factors. Further thermochronological constraints on the timing and rates of uplift in the Alaska Range will help with understanding the mechanism behind the tectonic history of the area of study and its effect and concurrently how the area is effected by climate change.