Degradation of moraine slopes with age in quaternary moraines of Eastern CA (2012)
Undergraduates: Sarah Cooley, Alison Domonoske, Erin Moore, Sagar Shukla
Faculty Advisor: Allen Glazner
Glacial moraines preserve evidence of former glaciers that advanced and retreated thousands of years ago. Observing moraines to determine past instances of climate change requires an understanding of moraine shape. By contrasting the slopes of moraines from various glaciations in the Sierra Nevada region (including the Tahoe (140,000 to 80,000 years ago), the Tioga (26,000 to 18,000 years ago) and the Little Ice Age (1350 to 1850 A.D)) we hope to determine the extent to which a correlation exists between moraine shape and age of glaciation.
In total we surveyed 7 moraines: 1 Little Ice Age, 3 Tioga, and 3 Tahoe. The Little Ice Age moraine ice side is the steepest with a slope angle of 33.0°. The 6 slope angle values of the Tioga moraines fall between 17.8° and 31.7°, whereas the 5 slope angle values of the Tahoe moraines fall between 12.6° and 26.2°.
Younger moraines have steeper maximum angles from the horizontal than older moraines, following the idea that erosion and weathering cause slopes to decrease over time. Our data show that the initial slope angle of a moraine is close to the angle of repose (34°), and over time erosion and gradual settling of the rocks cause the angles to decrease. We also found that the ice sides of lateral moraines and the non-ice sides of terminal moraines tend to be steeper. Our research demonstrates a method of differentiating moraines based on observing the extent to which erosional processes and weathering affect moraine slopes over time.