Wrangell-St. Elias National Park & Preserve

In 1980, the Alaska National Interests Lands Conservation Act was passed. Officially on November 12, 1980, President Carter designated 13.2 million acres of land to be created into Wrangell St. Elias National Park and Preserve. Wrangell-St. Elias National Park and Preserve has "...high mountain terrain, enormous glaciers and ice-fields, active thermal features, large canyons, extensive wildlife populations, and major historical mining features represent the significance of the park and preserve". This park is geologically important as it contains some of the biggest collections of glaciers and mountain peaks in the NPS.

Geographically, the park extends from the northern Pacific Ocean to interior Alaska. The formation of the park is estimated to be from the Triassic period, 258 mya when the Pacific Plate started to subduct beneath North America. Southern Alaska is composed of several different crustal fragments separated by major fault systems. These fragments make up the seven distinctive lithotectonic terrains. Notably, all of these terrains have their own geologic stratigraphy. This phenomenon is due to the process of accretionary tectonics. Which is when blocks of continental fragments collide with a continent and are now permanently attached. The terranes in Southern Alaska follow an arching pattern since terranes started docking in from the south.

In this picture: Yukon Tanana terrane began to collide with North America about 225 mya, and was attached to the continent by 180 mya. Wrangellia, Alexander, and Peninsular terranes slammed into North America around 110 to 85 mya, followed by the Chugach Terrane at about 67 mya, and then the Prince William terrane arrive 50 mya. The youngest terrane in Southern Alaska is the Yakutat Terrane which started to collide with North America 25 mya. It is still attached to the Pacific Plate, so it continues to smash into the continent. (NPS)

Located south of Yukon-Tanana, is the Wrangellia Terrain and it forms the basement of the Wrangell-Volcanic Field. Island-arc volcanic rocks (late Paleozoic-Tetelna Volcanics) lie at the base of the Wrangellia terrain. The volcanic unit is overlain by limestone, shale, and chert sedimentary units of the Permian age. Thought to have originated at lower altitudes prior to being transported northward and joined to mainland Alaska.

The volcanoes on Wrangellia were formed 5 mya due to the northward movement and subduction of the Pacific Plate and North American Plate. Which resulted in magma intruding through older terrane and creating the tall mountain ranges of Alaska. Furthermore, many of the peaks on top of the Wrangell Mountains were once active volcanoes. Currently, only one peak remains active; Mt. Wrangell. Found in the Wrangell Volcanic Field, this mountain is one of the largest andesitic volcanoes in the world and has produced lava flows up to 58 km long. It is currently active, but has not erupted for almost a century. Mt. Wrangell is a andesitic shield volcano and its peak formed a caldera in response to a past erruption that quickly emptied out a magma chamber.

Wrangell Volcanic Field is a "continental volcanic arc that developed along a convergent plate margin above a Yakutat block-related subduction zone" (NPS). The area is seismically active because the Yakutat terrane is still accreting towards North America. This leads to volcanism and with active fault zones there are frequent earthquakes.

Lillie, R. J. (n.d.). Convergent plate boundaries-accreted terranes. National Parks Service. Retrieved May 5, 2022, from https://www.nps.gov/subjects/geology/plate-tectonics-accreted-terranes.htm

U.S. Department of the Interior. (n.d.). NPS geodiversity Atlas-Wrangell-St. Elias National Park, Alaska (U.S. National Park Service). National Parks Service. Retrieved May 5, 2022, from https://www.nps.gov/articles/nps-geodiversity-atlas-wrangell-st-elias-national-park-alaska.htm

U.S. Department of the Interior. (n.d.). Geology. National Parks Service. Retrieved May 5, 2022, from https://www.nps.gov/wrst/learn/nature/geology.htm#:~:text=Geology-,Wrangell%2DSt.,plate%20tectonics%2C%20and%20quaternary%20geology.

U.S. Department of the Interior. (n.d.). Volcanic landforms: Intrusive igneous. National Parks Service. Retrieved May 5, 2022, from https://www.nps.gov/subjects/geology/intrusive-igneous-landforms.htm

U.S. Department of the Interior. (n.d.). Volcanoes. National Parks Service. Retrieved May 5, 2022, from https://www.nps.gov/wrst/learn/nature/volcanoes.htm

Wrangell - St Elias National Park and Preserve Geology. US. (n.d.). Retrieved May 5, 2022, from https://www.us-parks.com/wrangell-st-elias-national-park-and-preserve/geology.html