4-D ANALYSIS OF GRIZZLY GLACIER, TRINITY ALPS, CALIFORNIA (WORKING)

Grizzly Glacier is the lowest elevation glacier remaining in California. It is located just below the crest of the Trinity Alps in Northwestern California. Its modern ELA is at approximately 2,520 m. In the Little Ice Age (LIA) it had a significant advance with ice making it into Grizzly Lake (Graham, 2013). This study focused on determining the volume of the modern glacier, along with the timing of retreat since the last LIA maximum (103-163 YBP).

The volume was calculated by surveying the surface (2012, 2013) with a differential GPS system, and measuring the depth at various locations with another GPS and a measuring tape. These were combined into Triangular Irregular Networks and a volume was calculated from these using ArcMap 10.1.

The timing of retreat was analyzed by looking at the youngest LIA moraine (Graham, 2013), and looking at historic imagery to determine whether the post-LIA retreat was rapid, recent, or constant. It appears as if much of the glacier’s retreat occurred before 1955 (the oldest aerial image available). Justin Garwood (unpublished) contributed a GPS survey from 2009, which indicates that the glacier has not changed significantly in the last 4 years. However, the calculated volumes from 2012 to 2013 indicate a 15.5% reduction.