Heceta Island is part of Alexander Terrane. It is a large crust fragment formed on a tectonic plate. The fragment sheared off the oceanic Pacific Plate and was deposited onto the continental North American Plate somewhere between the middle Jurassic and Late Cretaceous time (Kovarik, 2009). According to Kovark (2009), “The process of accretion resulted in fragmentation and smearing of sections of the terrane northward, while other portions remained in place” (p. 9). Read more about this process at the National Park Service.The island is next to a transform boundary that runs North and South. Seismic ExplorerThis image shows multiple locations of fragmentation. That could be due to strike slips near the fault line -Google EarthHere you can see it from a different perspective -Google Earth
Heceta Island has 5 volcanos nearby
The oldest is Hoodoo Mountain. Hoodoo is 110 miles to the Northeast and erupted over 9500 years ago. Seismic ExplorerMount Edgecumbe is 120 miles away from the Northwest and last erupted 4,241 years ago. Mount Edgecumbe is a sacred Tlingit Mountain. Seismic ExplorerEdziza (Crud Z eye Z uh) Mountain is 175 miles away to the Northeast and last erupted in the year 950. Edziza (Crud Z eye Z uh) is an ancient source of obsidian that was used for tools and weapons. Seismic ExplorerThe Tseax (SEE-aks) River Cone is 180 miles away from the Southeast and last erupted in 1690. Seismic ExplorerThe Iskut-Unuk (Kiss cut you nuck) River Cones is located 120 miles away to the Northeast and last erupted in 1904. The Tlingit have oral history about this being one of the tall locations people fled to during the great flood. Seismic Explorer
Glacial activity
I chose this 1984 image from Google Earth because you can see the glacial flow N-NW of Juneau, as well as in a few other spots. All of Southeast Alaska’s landscape has this similar look. You can see ocean inlets that are formed from glacial troughs’. I think these are called fjords. The telltale signs of glacial erosion are all over. I can see cirques and aretes stand out as the obvious details, but you can find horns and tarns. -Google EarthHeavy ablation at the lower ends has caused a quick retreat between 1984 and 2020. These images were both taken in December to show a fair comparison. -Google EarthThis last image has a couple of features that caught my eye. I see what may have been an esker. Next to it, you can see a feature that appears to be an alluvial fan. It may be underwater because ocean levels rose after it was created.
