GROUNDED ICEBERG WAKE PATTERNS FOLLOWING CATASTROPHIC FLOOD EVENTS IN SOUTHCENTRAL ALASKA

Glaciated areas in Southcentral Alaska are prone to unstable slopes and large quantities of meltwater, which can result in unpredictable and sometimes catastrophic flooding events such as jökulhlaups (glacial outburst floods) and tsunamis generated by landslides occurring in proglacial bodies of water. These flood events differ in duration and origin, but both can alter the landscape and pose a risk to local populations.

Active glaciers often terminate into a body of water such as a proglacial lake, river, or ocean and can contain icebergs of varying size and quantities. Transported during a catastrophic flood event, the large size of the icebergs results in them becoming grounded while sediment is still being transported. Deposition in the area around the iceberg results in a depression after the iceberg melts. The obstruction to floodwater flow that the iceberg creates leaves distinct wake patterns in the deposited sediment visible on lidar. These obstacle depressions and wake patterns have been minimally characterized by the scientific community but can contain detailed sedimentological information about conditions of the later stages of the flows.

In this study we interpret and characterize the grounded iceberg wake patterns in two locations in Southcentral Alaska using lidar imagery. The first location is adjacent to Grewingk Lake, a body of water fed by the Grewingk glacier that was overrun by a landslide-generated tsunami in 1967. The second location is the Matanuska River valley, fed primarily by the Matanuska glacier, which shows evidence of jökulhlaups within the last 1000 years. Iceberg depression and wake characteristics that we measured in ArcGIS Pro include length, width, depth, shape, flow direction, position along flow, and other notable features. We also compared wake patterns visually to identify trends between individual features and between the two study areas. Results of the depression and wake characteristics indicate flow direction and velocity changes along the flood path, which can assist preparation and response to future catastrophic floods.