Sunday, January 18, 2015

Cenozoic geology in the National Parks, part II: igneous

Quite a number of NPS units record some form of Cenozoic igneous activity, from the obvious (active volcanoes) to the subtle (rock formations that are composed of volcanic debris, or ancient lake deposits that were laid down after a lava flow blocked a river). Restricting the category to just those with Cenozoic igneous rocks still nets quite a few. I decided to go with just those where the igneous rocks are responsible for a headline attraction, or make up a significant part of the bedrock. I've got both a map and a spreadsheet of igneous activity in geologic time, and as you go through you may notice a few patterns. First, a lot of the featured parks have fairly recent activity, roughly Miocene to the present, a span of about 23 million years. Part of this is a natural bias of erosion (younger, less-eroded igneous features are more impressive than old, worn-down features), and part of this is due to the timing of the eruptions themselves. Volcanism on the Rio Grande Rift of New Mexico began shortly before 23 Ma, Great Basin volcanism began around the same time, the Yellowstone Hotspot trail has only been traced back around 16 million years, and the volcanoes of the Hawaii parks only poked out from the ocean during the Pleistocene. Another feature is location. There is a nice arc through southern Alaska, and clusters in northern California–southern Oregon, around the Great Basin–Mojave Desert, in New Mexico, and eastern Idaho–northwestern Wyoming, which correspond to centers of igneous activity.

Take a deep breath: 1. Mount Rainier National Park (NP); 2. Crater Lake NP; 3. Lava Beds National Monument (NM); 4. Lassen Volcanic NP; 5. Pinnacles NP; 6. Devils Postpile NM; 7. Death Valley NP; 8. Channel Islands NP; 9. Santa Monica Mountains National Recreation Area (NRA); 10. Mojave National Preserve (NPRES); 11. Joshua Tree NPRES; 12; Lake Mead NRA; 13. Sunset Crater NM; 14. Organ Pipe Cactus NM; 15. Chiricahua NM; 16. Gila Cliff Dwellings NM; 17. El Malpais NM; 18. Valles Caldera NPRES; 19. Bandelier NM; 20. Capulin Volcano NM; 21. Big Bend NP; 22. City of Rocks National Reserve; 23. Craters of the Moon NM & Preserve; 24. Yellowstone NP; 25. Devils Tower NM; 26. Aniakchak NM & Preserve; 27. Katmai NP & Preserve; 28. Lake Clark NP & Preserve; 29. Wrangell-St. Elias NP & Preserve; 30. Haleakalā NP; 31. Hawai'i Volcanoes NP

Cascade Range parks:
Crater Lake National Park: Mount Mazama erupted around 7,700 years ago, leading to the titular Crater Lake. There are also older volcanic rocks, from the Middle and Late Pleistocene.
Lassen Volcanic National Park: Numerous eruptions have occurred from the Pliocene to the present, producing shield volcanoes, stratovolcanoes, cinder cones, and other features.
Lava Beds National Monument: Volcanic eruptions here began about 2 million years ago, during the Early Pleistocene, with Medicine Lake Volcano being a major contributor.
Mount Rainier National Park: Mount Rainier is an active volcano, and has been active since the Early Pleistocene.

Western California: The igneous activity of these three parks dates to the Miocene and shows interesting tectonic influences.
Channel Islands National Park: Each of the five islands in Channel Islands National Park has volcanic rocks that were erupted during the Early and Middle Miocene. Interestingly, the Channel Islands are not volcanic islands. The northern four are in fact part of a rotated crustal block formerly located far to the south, and their volcanics are related to the Conejo Volcanics of Santa Monica Mountains National Recreation Area.
Santa Monica Mountains National Recreation Area: The Conejo Volcanics were produced during the Early Miocene, from a source near Newbury Park. The volcanic activity produced a large submarine cone that eventually reached above the surface, like the Hawaiian Islands.
Pinnacles National Park: The Pinnacles of Pinnacles National Park are formed from the Early Miocene Neenach Volcanics. The original volcano has been bisected by the San Andreas Fault. Part of the volcano stayed home, near Lancaster, and part of it traveled north and became the Pinnacles.

Great Basin/Mojave Desert/Sonoran Desert:
Several parks in the Mojave Desert and Great Basin region have long volcanic histories, usually beginning in the Miocene with the onset of Basin and Range tectonic activity. They include Death Valley National Park, Joshua Tree National Preserve, Lake Mead National Recreation Area, and Mojave National Preserve. Igneous rocks have been erupting and intruding into Death Valley National Park for practically the entire Cenozoic. Associated with these volcanics are a number of volcanically sourced localized sedimentary formations. Other parks, with similar but smaller-scale activity, and thus not on the map or spreadsheet, include Grand Canyon National Park and Zion National Park.
Chiricahua National Monument: Chiricahua's features are mostly derived from Late Oligocene volcanic activity in the Turkey Creek Caldera. "Caldera", for those of you not familiar with the lingo, means "there was a volcano here, but it erupted its magma and then collapsed".
Devils Postpile National Monument: The namesake postpile was formed by a basalt flow dating to the Late Pleistocene.
Sunset Crater National Monument: The Sunset Crater cinder cone erupted slightly less than a thousand years ago.
Organ Pipe Cactus National Monument: Much of the bedrock of this monument is composed of Early and Middle Miocene igneous rocks, including the Ajo volcanic field.

New Mexico: The Rio Grande Rift has been making an effort to divide New Mexico and southern Colorado for tens of millions of years. In northern New Mexico it ran across an old weakness in the crust known as the Jemez Lineament, which boosted volcanic activity throughout that part of the state. The rift meets the lineament about where Valles Caldera is, Valles Caldera happening to be the tombstone of one of the most generous volcanoes known on Earth.
Bandelier National Monument and Valles Caldera National Preserve (current link, no NPS page yet): Bandelier National Monument is essentially made up of igneous rocks produced between the Late Oligocene and Late Pleistocene, erupted from vents in and near its next-door neighbor, Valles Caldera National Preserve (just transferred to the NPS). Valles Caldera, the namesake feature, was active during the Pleistocene.
Capulin Volcano National Monument: The Capulin Volcano cinder cone erupted approximately 60,000 years ago, during the Late Pleistocene.
El Malpais National Monument: The Zuni–Bandera Volcanic Field was active here from the Middle Pleistocene to a few thousand years ago.
Gila Cliff Dwellings National Monument: The monument happens to be located in the southeastern part of the Gila Cliff Dwellings caldera, in the Mogollon–Datil volcanic field. The caldera had its explosive moment at about the Early–Late Oligocene boundary, ~28 Ma.

Yellowstone and vicinity:
City of Rocks National Reserve: Most of the city of City of Rocks is composed of granite that intruded during the Oligocene, about 28 Ma.
Craters of the Moon National Monument and Preserve: This unit is based around latest Pleistocene and Holocene volcanic flows.
Yellowstone National Park: Although justifiably famous for the Yellowstone Caldera, which produced three massive eruptions during the Pleistocene, Yellowstone National Park is also marked by a previous volcanic episode, during the Early and Middle Eocene. One of the most lasting reminders of this volcanic activity is the "petrified forests" of Yellowstone, found in the northeastern and northwestern parts of the park in the Lamar River and Sepulcher formations. Two chains of volcanoes oriented northwest-southeast erupted here during the Eocene. Some people get worked up over the possibility of the Yellowstone Caldera erupting again, but I figure enough time may have gone by so that the next big one will be in a new location to the northeast. This is better, because... Yellowstone won't get a new giant crater, just buried under a mountain of ash? It's kind of hard to sugarcoat a Yellowstone-magnitude eruption.

Southern Alaska: Active volcanoes abound in southern Alaska.
Aniakchak National Monument and Preserve and Katmai National Park and Preserve: These two parks feature the Meshik Volcanics (Late Eocene–Early Oligocene), more recent intrusive rocks (Late Miocene–Pliocene), and Quaternary volcanic activity from the Aleutian Range. Both parks are named for active volcanoes.
Lake Clark National Park and Preserve: This park is also in the Aleutian Range, with Mount Iliamna and Mount Redoubt being its two most famous volcanoes.
Wrangell-St. Elias National Park and Preserve: This park hosts the Wrangell Volcanic Field, which has been active since the Late Oligocene.

Haleakalā National Park and Hawai'i Volcanoes National Park: These two Hawaiian parks are known for their Quaternary volcanoes, with activity in Haleakalā National Park beginning in the Early Pleistocene and activity in Hawai'i Volcanoes National Park beginning in the Middle Pleistocene.

Big Bend National Park: Cenozoic Igneous activity occurred here primarily during the Early Oligocene.
Devils Tower National Monument: The famous eroded igneous tower intruded into the surrounding bedrock during the Early Eocene.

A thumbnail of volcanic activity, time, and place. Click to embiggen.

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