Evolution of ogives on Gilkey Glacier, Alaska

• Main Author: Hill, Ann
• Format: Text
• Language: unknown
• Published: Creative Matter 2018
• Subjects: Earth Sciences; Environmental Sciences; Geology; Juneau Icefield; glacier; glaciers; Alaska
• Online Access: https://creativematter.skidmore.edu/geosci_stu_schol/1; https://creativematter.skidmore.edu/cgi/viewcontent.cgi?article=1000&context=geosci_stu_schol

Periodically since 2001, the Juneau Icefield Research Program has collected data measuring the elevation of a longitudinal transect on the surface of Gilkey Glacier, Alaska, using a survey-grade GPS. This data record allows for analysis of the shape of the glacier as it changes over time. The surface of Gilkey Glacier exhibits ogives, arcing structures that form as a result of extreme compression at the start of the transect, located at the top of the glacier and the base of the Vaughan Lewis Icefall. The ogives are comprised of alternating dark colored trough and light colored peaks. The troughs travel through the icefall during the summer, while the peaks travel through the icefall in the winter, resulting in one wave being produced each year. Having a record that spans 16 years allows for analysis of the ogives to gain insight into the dynamics at play on the glacier. This is achieved through calculating changes that occur both with distance along the transect, as well as over time, and includes values of the elevation, wavelength, amplitude, longitudinal surface strain rate, and width. Also, an estimate of the annual average surface velocity can be made by tracking ogives down glacier through time, as one ogive is produced each year. Both the surface elevation, and the wave amplitude decrease through time, and with distance along the transect. The longitudinal surface strain rate tends to be positive at the start of the transect, and negative down-glacier, resulting in an average of 0 a-1 across the entire study area. The wavelength increases along the transect, but reaches its maximum value at around 1 km down-glacier. The width decreases along the transect, as it is confined by the other glaciers also flowing into Gilkey Trench. The annual average surface velocity follows different trends over time, depending on how the data are analyzed. The increase in wavelength, and the decrease in width both suggest that Gilkey Glacier is undergoing extension. On the other hand, the decrease in longitudinal surface strain rate along the length of the glacier, and the concave up geometry of the surface both indicate a compressional regime, however, these signals are weak.