Virtual Volcano Vacation #121 WINNER! – Aniakchak

Aniakchak caldera as viewed through The Gates. Photo by Troy Hamon / U.S. National Park Service via nps.gov

Oddly enough I was not necessarily looking for a volcano when I found this week’s hiding place. While looking over a list of U.S. National Parks and National Monuments on Wikipedia (as a part of the political activist aspect of Li’l Volcanohead which a few of you may be familiar with), I saw the name and recognized it from the A-to-Z list of volcanoes on Global Volcanism Program’s site, but had somehow never actually had a look at the volcano before. I guess you could say he got “lost in the crowd”, but that can happen to a volcano when one is just one of 62 volcanoes of Alaska’s Aleutian Arc, such as is the Aniakchak caldera.

You might say that Aniakchak is Alaska’s best kept secret. Though the area was surely familiar to the native inhabitants of the area, perhaps even known to them for its fiery nature, it was not formally recognized as a volcano until 1922. The discovery began with a group of geographers who were mapping the area and plotting mountains around the rim when they noticed a circular pattern. A group of USGS geologists would later climb up those slopes and look into the caldera with all its volcanic features, which may have come as quite a surprise.

1977 aerial photo of Aniakchak caldera as seen from the west – by M. Williams / U.S. National Park Service – public domain image courtesy AVO/USGS

More on what they saw in a moment, but first, a little bit about how this caldera was born. Near the very start of the Holocene, a 2,130 m high volcano designated Aniakchak I was active near the tall cone that occupies the present-day caldera. It is believed to have undergone a VEI 6 eruption which formed a small caldera and deposited a layer of ignimbrite and welded tuff around 6300 BCE (± 1250 years), but the “big one” would be around 1640 BCE, reducing that mountain’s hight by more than 900 m and creating a 10 km wide caldera. Pyroclastic flows traveled 50 km north to the Bering Sea as well as south to the Pacific Ocean, and tephra from the eruption made its mark in ice core samples.

The modern caldera is just about completely ringed by walls that rise between 610 and 1,341 m above the caldera floor. In the northeast corner lies the 3.2 km long Surprise Lake, which is actually what remains of a once larger and deeper snow-fed lake which occupied the whole caldera at greater depth.  Some time around 1,850 years ago, perhaps due to hydraulic pressure, the lake breached the caldera’s east side and the water carved its way to the Pacific Ocean, becoming the Aniakchak River. The V-shaped breach through which the river passes is now called The Gates.

Landsat 7 natural colour image of Aniakchak caldera from 15 September 2000 – image via EarthObservatory.NASA.gov

All of Aniakchak’s volcanic features lie within the caldera along ring fractures. In the centre and perhaps the most noticeable features is a Vent Mountain, a cone 2.5 km wide at its base that rises 430 m above the floor of the caldera. In the northwest part of the caldera, Half Cone is the remnants of a 1540 CE plinian VEI 4 eruption that partially destroyed what (in this volcanohead’s opinion) would have likely been called Whole Cone, filling the caldera floor with meters-thick pyroclastic material and ultimately choking the cone’s basin with a lava flow. There are other domes and maars around the caldera as well, most with rather unimaginative but appropriately descriptive names.

Map of Aniakchak caldera’s features – courtesy AVO/USGS

Aniakchak’s only historically observed eruption took place in 1931, and was chronicled by a Jesuit priest, Fr. Bernard Hubbard. He wrote “A small but impressive explosion pit was added to the pockmarked caldera floor that year. Many thousands of tons of ash lay strewn within the caldera and scatttered up to 30 miles away over the small villages.” This pit now bears the name 1931 Crater.

Aniakchak – 1931 Crater in foreground with Half Cone on the left and Surprise Lake in the background to the right – Image by T.A. Plucinski courtesy AVO/USGS

Today, the caldera and surrounding area are part of the Aniakchak National Monument and Preserve, one of the US National Park Service’s wildest and least-visited of its 87 National Monuments. Its remoteness as well as the high chance of bear encounters perhaps deters all but the most hardy tourists, but for a volcano-vacation it would seem an ideal spot.

This video not only shows off what there is to see and do at Aniakchak, but I think the song has just become Li’l Volcanohead’s new theme music.

Congratulations, Glenn, for finding me. I am sure the bears will be glad to have their nice quiet peaceful volcano returned to them, and somewhere else in the world there is new trouble waiting for me to get into it. Be sure to come back this Monday (despite the holiday) and join me on a new adventure at a new volcano.

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