Discover Alaska and Explore the Geodiversity and Fossils of Aniakchak National Monument and Preserve
- Wayne Munday
- Apr 10
- 5 min read
Sip back and discover Alaska and explore the geodiversity and fossils of the Aniakchak National Monument and Preserve. This ancient landscape encompasses over 2,442 km² and has been shaped by tectonic, volcanic, sedimentary and glacial activity spanning over 160 million years. Its Mesozoic Era fossil record is primarily from the Jurassic and Cretaceous Periods - though there is still a lot more research and fossils to be found yet. The Aniakchak National Monument and Preserve is located in south west Alaska on the Alaska Peninsula bordering the Pacific coastline dominated by the Aleutian Range of mountains with the Bering Sea to the west and the Gulf of Alaska to the south. At over 650 Km from Anchorage the Aniakchak National Monument and Preserve is very isolated and really only accessible by sea plane or boat. This is no wonder to why the Aniakchak National Monument and Preserve receives the fewest visitors of any park in the USA.
Apart from the amazing landscape and fossil record the remoteness of the Aniakchak National Monument and Preserve supports a rich biodiversity of large land mammals such as Brown Bears, Moose, Caribou, Wolves, and Wolverines. Other mammals found here include Red Foxes, Arctic Ground Squirrels, River Otters, Porcupines and Beavers. Along the coastline marine mammals such as harbour Seals, Sea Otters, and Sea Lions thrive in the area’s rugged bays and inlets.
Aniakchak is an important habitat for waterfowl and migratory birds and a the hunting ground for bald eagles known as "fish eagles" or "sea eagles" because fish often comprise the majority of their diet. The Aniakchak River is an essential spawning ground for sockeye salmon.
Many whale species migrate through the waters off the Alaska Peninsula and the best time for whale watching is between May and September to watch the Grey Whale, Humpback and Orca whales make their seasonal journeys between feeding and breeding grounds. They are also joined by other species including the Baird's Beaked, Bowhead, Cuvier's Beaked, Fin, Minke, North Pacific Right, Sei, Sperm and Stejneger's Beaked whales to feed in the open water during the Summer.
The Mesozoic Era rock formations of the Hoodoo Formation, Naknek Formation, Chignik Formation preserve numerous assemblages of marine invertebrate fossils, dinosaur tracks and plants. More recent rock formations such as the Tolstoi Formation dating across the Paleocene and Eocene Epochs of the Cenozoic Era between 66 - 50 million years ago indicate that the Alaska Peninsula had a subtropical environment.
The Late Cretaceous Hoodoo Formation on the Alaska Peninsula indicates a marine environment and fossil record yields clam like bivalves called pelecypods and ammonites. The later Chignik Formation dates to the Maastrichtian Stage of the Late Cretaceous between 72.1 - 66 million years ago. At the time the Alaskan Peninsula was experiencing a cyclical or continuous looping sequence of having a shallow marine to continental alluvial coastal plain known for plant fossils forming the high-volatile B bituminous coal bearing seams of the Herendeen Bay-Chignik Coal Fields.
This river and nearshore sediment is also known for its ichnites the trace fossil footprints or dinosaur tracks and particularly those of of the duck-billed hadrosaurid dinosaurs. The oldest rocks in the region belong to the Naknek Formation dating to the Late Jurassic 164 - 145 million years ago and known for its fossils of clams known as Buchia as well as ammonites and marine reptiles such as the plesiosaur.
The Aniakchak National Monument and Preserve has a dominant geological feature in the 10.5 Km wide Aniakchak Crater. This is a collapsed caldera of the ancestral Aniakchak volcano that once towered 2,100 meters above sea level and collapsed approximately 3,660 years ago during the Aniakchak II eruption. All that is left todays is the 1,341 meter summit of the caldera filled with a lake called Surpise Lake. Also, the surrounding lands have a geomarker within the geological record that marks the eruptions with an extensive layer of volcanic material called ignimbrite covering 2,500 km² reaching as far north as the Seward Peninsula.
The landscape suggests that pyroclastic flows from the Aniakchak II eruption likely triggered a tsunami on the northern shore of Bristol Bay because pumice created when super-heated and highly pressurised rock is rapidly ejected from a volcano is found to be interbedded with peat layers as high as 12 meters above mean high tide. It is thought that the pumice and ash fall was transport inland by the tsunami wave.
Numerous smaller volcanic features have developed around the Aniakchak Crater including lava domes and cinder cones. Still today geothermal activity continues within the caldera with numerous warm springs entering Surprise Lake and emitting geothermal steam.
More recently glaciation has been a dominant force in sculpting the rugged and complex topography of the Alaska Peninsula landscape. The Alaska Peninsula has Pleistocene fossils including a diverse assemblage of Ice Age megafauna including woolly mammoths, steppe bison, horses, short-faced bears, and wolves. Repeated glacial advances and retreats during the Pleistocene Epoch left behind a variety of glacial features, including moraines, outwash plains, and glacially carved basins.
Alaska’s official state fossil is the woolly mammoth (Mammuthus primigenius) a species from the Pleistocene age. While Alaska does not currently have an official state dinosaur there has been a proposal to name Nanuqsaurus (meaning "polar bear lizard") a small theropod and tyrannosaur relative found on Alaska’s North Slope as the state dinosaur.
Alaska has a number of fossil sites found within the Fairbanks and Klondike mining districts, the Seward Peninsula’s Trail Creek Caves and the Yukon River has its very own "Boneyard". Other significant locations are the Kikak-Tegoseak bonebed with Pachyrhinosaurus fossils, Fossil Point in Cook Inlet for marine fossils, and Glacier Bay National Park, which preserves plant fossils from the Yakataga and Frederika formations. Evidence of human hunting of mammoth, bison, and caribou bones suggests human presence in the region during the late Pleistocene. Finally, proboscidean fossils of large mammals such as mammoths and mastodons on the Bering Land Bridge supports the theory that in the pursuit of food and more favourable climate conditions animals as well as early humans migrated into Alaska from Asia when the land bridge connected north eastern Siberia to western Alaska during periods of lower sea levels.
