Active Seismic Studies in Lemon Creek Valley Glacier, Juneau, Alaska: Characterization of Subglacial Sediments to Understand Glacier Dynamics

• Main Author: Gonzalez, Lucia Fernanda
• Format: Text
• Language: English
• Published: ScholarWorks@UTEP 2020
• Subjects: Geophysics and Seismology; Juneau Icefield; Lemon Creek; glacier; Alaska
• Online Access: https://scholarworks.utep.edu/open_etd/3163; https://scholarworks.utep.edu/cgi/viewcontent.cgi?article=4162&context=open_etd

Deformation and flow properties of subglacial sediments as well as the presence and volume of water at the ice/bed interface strongly influence glacier dynamics. Studies of Lemon Creek Glacier, a small temperate valley glacier in the Juneau Icefield, near Juneau, Alaska, have shown that the glacier is rapidly retreating, with a negative mass balance every year since 1957. However, the bed topography and properties of subglacial sediments at the base of Lemon Creek Glacier remained unknown until now. In this project, we process and interpret ~1-km-long NW-SE trending active-source seismic reflection profiles collected during June and July 2017 near the centerline of Lemon Creek Glacier. We first use reflection seismic data processing to produce common depth point (CDP) seismic images of the ice-bed interface. Our seismic profiles, roughly parallel to the ice flow direction, show a smooth but complex ice-bed topography. We observe two over-deepening features under Lemon Creek Glacier with maximum depths of ~285 m near the NW end of the line and ~370 m near the SE end of the line. We then perform an Amplitude vs Angle (AVA) analysis, following the multiple-path method for the calculation of source amplitude, to characterize subglacial sediments at the base of Lemon Creek Glacier. The seismic amplitude analysis indicates that dilatant tills are predominant at the ice-bed interface along with some dewatered tills and bedrock. However, a highly complex topography, crevassing and ground roll (surface wave) noise undermined our efforts to constrain material properties at near-normal incidence, producing results only for large incidence angles. We conclude that AVA in this glacier using the multiple-path method for source amplitude is challenging, suggesting that other approaches are needed to characterize materials beneath Lemon Creek Glacier.