Last updated: April 17, 2023
Volcanic necks and plugs are the solidified remains of volcanoes’ conduit and plumbing systems that remain after the rest of a volcano has been eroded away. Solidified conduits are usually more resistant to erosion than the surrounding volcanic edifice which may have consisted of loose tephra or hydrothermally altered rock.
No real differences exist between volcanic necks and plugs. Both are roughly cylindrical in shape and stand out in relief about the surrounding countryside. They appear as vertical pipelike bodies of dense rock that can form rock pinnacles or spires that may stand up to hundreds of feet (meters) in height.
Sometimes systems of radial dikes that were also part of the volcano’s plumbing system are found in association with volcanic necks.
Technically, volcanic necks and plugs are intrusive because they consist of rock that solidified within the Earth. But they were once part of volcanoes and solidified at very shallow depths, potentially even ascending to the level of the former eruptive vent.
National Park Volcanic Necks or Plugs
At least ten units of the National Park System contain volcanic necks or plugs.
Big Bend National Park
Volcanic activity took place in the Chisos Mountains in Big Bend NP during the Cenozoic. Several features which are likely volcanic necks are found in the park.
Devils Tower National Monument
Devils Tower is an enigmatic feature whose origin is not completely understood. The tower stands about 867 feet (265 m) tall and formed about 40.5 million years ago. Devils Tower may be the result of a shallow intrusion, or it may be a volcanic neck. One hypothesis is that is the remnant of a maar-diatreme volcano.
Grand Canyon National Park
Volcanic eruptions occurred in the western part of Grand Canyon between about 75,000 and 725,000 years ago. One imposing volcanic neck even sticks above the Colorado River just above one of the most difficult rapids in the entire canyon.
Grand Canyon-Parashant National Monument
The oldest volcanic activity that occurred in Grand Canyon-Parashant NM occurred in the Grand Wash Volcanic Field. It was active approximately between 4 and 6 million years ago.
Katmai National Park
Devils Desk is a volcanic neck in Katmai National Park. Erosion has removed most of the composite volcano leaving only the conduit and radial dikes. The volcano was active nearly 250,000 years ago.
National Park Sites with Volcanic Necks or Plugs
Ice Age Floods National Geologic Trail (IAFL), WA, OR, ID, and MT—[IAFL Park Home]
Lewis & Clark National Historic Trail (LECL), IA, ID, IL, IN, KS, KY, MO, MT, NE, ND, OH, OR, PA, SD, WA, and WV—[LECL Park Home]
- big bend national park
- crater lake national park
- craters of the moon national monument & preserve
- devils tower national monument
- grand canyon national park
- grand canyon-parashant national monument
- ice age floods national geologic trail
- katmai national park & preserve
- lewis & clark national historic trail
- sequoia & kings canyon national parks
- volcanic necks
- volcanic plugs
- erosional volcanic landforms