Basaltic Lava Flows

Photo of molten lava flowing across the ground.
‘A‘ā lava flows erupting from Mauna Loa in 1984.

USGS photo.


Most lava flows, including the ones from Kīlauea and Mauna Loa volcanoes in Hawai’i Volcanoes National Park, have basaltic compositions. The low silica concentrations in these lavas mean that they are highly fluid (e.g., have low viscosity) and they flow easily, forming lava flows that may travel great distances from the vent where they were erupted to cover broad areas of land.

Basaltic lava flows may be erupted from shield volcanoes such as in Hawai’i, from vents at the base of a cinder cone such as Sunset Crater Volcano National Monument in Arizona, fissure volcanoes such as at Craters of the Moon National Monument in Idaho, and in monogenetic volcanic fields like at El Malpais National Monument in New Mexico.

Basaltic lava flows usually either have pahoehoe or ‘a‘ā morphological forms. The surfaces of pahoehoe lava flows are smooth, ropy, or billowy, and ‘a‘ā flows are rough and clinkery.

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Basaltic lavas are emitted in effusive (Hawaiian style) eruptions where they either ooze out from vents or are ejected in lava fountains that may be propelled a hundred feet (30 m) or more into the air before landing and starting to flow as molten rock. Lavas that are discharged at high rates generally travel faster and further from their vent than ones that are erupted at lower rates. Topography, especially the steepness of slopes on which lavas flow, also greatly impact the speeds and distances that they can travel.

Basaltic lava flows generally travel as either:

  • broad sheets,

  • in channels,

  • or through lava tubes.

Sheet-fed Lava Flows

Sheet-fed flows do not have any surface channels, and flow as a single body of lava. They generally occur during eruptions with high discharge rates and usually in high volume eruptions. Sheet-fed lava flows also may occur on areas of gentle slopes. Both pāhoehoe and ‘a‘ā lavas may be sheet-fed. Sheet-fed pāhoehoe lava flows may be inflated since the surface crust may be cooled while lava is still being fed into the flow.

Photo of lava flow.
An active sheet lava flow during the 1984 eruption of Mauna Loa in Hawai’i Volcanoes National Park.

NPS Photo by B. Seiber.

Channel-fed Lava Flows

Some lavas travel primarily in surface channels that develop between levees made of chilled portions of the flow. Levees may be higher than the molten stream of lava when discharge rate decreases from a higher initial rate. And channel levees may be overtopped if the discharge rate increases or if an obstruction in the channel forms downstream. Channels in lava flows sometimes follow preexisting topographic lows like river valleys or form novel ones based on the topography of the chilled flow surface. Both pāhoehoe and ‘a‘ā lavas may flow in channels.

Aerial photo of molten lava flowing in a channel.
Channelized lava flow in Hawai’i Volcanoes NP during the 2018 eruption of Kīlauea.

USGS photos.

Thermal image of a lava flow channel.
Thermal image of a channelized ‘a‘ā flow in 2011. The channel leads from the fountains at the vent to a delta-like flow front.

USGS image.

Tube-fed Lava Flows

Lava tubes are conduits in the interior of lava flows through which molten lava travels. A lava tube may form by the crusting over of a surface lava channel or when the chilled surface of a flow insulates channels flowing lava within it. Lava may flow very rapidly inside tubes on steep slopes as it remains very hot and fluid in the interior of a flow. Lava flowing in tubes in Hawai’i Volcanoes National Park can flow as fast as 19 miles (30 km) per hour.

Lava tubes may drain at the end of the eruption or when lava is diverted elsewhere in the flow. Lava tubes may also collapse during the eruption or after it ends.

Some lava tube caves are many miles (kms) long, such as ones in Lava Beds National Monument and El Malpais National Monument.

Lava tubes are usually only found in pāhoehoe flows.

Photo of molten lava flowing beneath a hardened lava surface.
A skylight showing an active lava tube during the 2014 eruption of Kīlauea in Hawai’i Volcanoes National Park.

USGS photo.

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Basaltic Lava Flow Features

Basaltic lava flows are more than just seas of black rock. Solidified flows have features that provide information about their eruptions and emplacement.

► Breakout

A breakout is a new area or region of a lava flow formed where lava from the molten interior of a previously formed lobe breaks out through its sides or upper margin to create a distinct lava flow advance.

Aerial photo of recent lava flows.
A breakout from a lava flow in 2016 from Kīlauea in Hawai’i Volcanoes National Park.

USGS photo.

► Lava Flow Fields

A lava flow field is a body of lava, consisting of one or more lava flows, that is the product of a single eruption.

Aerial photo of a hillslope covered by a lava flow.
A lava flow field formed during the 2018 eruption of Kīlauea in Hawai’i Volcanoes National Park. Lava channels are the darker area of the flow field. Photo taken in 2021 when steam was visible.

USGS photo by K. Mulliken.

► Surface Features

Basaltic lava flows, particularly pāhoehoe flows, may have a variety of surface features including hornitos, levees, tumuli, pressure ridges, and squeeze-ups.

Photo of a contact between ropy and blocky lava rocks.
Highly vesiculated region near the top of a basaltic lava flow in Craters of the Moon National Monument. The uppermost part of the flow with the ropy pāhoehoe was rapidly quenched, which prevented the formation of vesicles.

Photo by John St. James on Flickr.

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► Lava Tubes

Lava tubes or collapsed lava tubes may be present in basaltic lava flows.

Photo of a hole in hardened surface lava where molten lava can be seen flowing beneath.
View into an active lava tube through a skylight. The lava stream is flowing from lower left to upper right.

USGS photo.

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► Inflation Structures

Sheet-fed pāhoehoe flows may inflate after their crusts have solidified and their flow front has stopped advancing or cannot move fast enough to accommodate the rate of lava supply. Inflation thickens the lava flows and forms surface features such as tumuli and inflation pits.

Photo of lava flow.
The left side of the photo shows an older lava flow that has inflated so that it is now 10 ft (3 m) above the ground surface. On the right, new pāhoehoe lava breakouts. Photo taken in 2016 during the Kīlauea eruption.

USGS photo.

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► Tree Mold Fossils

Lava flows may surround either standing or fallen trees, leaving behind tree mold fossils.

photo of lava rock with the imprint of tree bark.

USGS photo.

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► Kīpukas

Kipukas are areas that are surrounded by lava flows. In areas with young lava flows, they may be islands of vegetation and animal habitat surrounded by relatively inhospitable rock.

Photo of areas of barren lava flows surrounding islands of older vegetation.
Kīpuka formed during the 2018 lower East Rift Zone eruption of Kīlauea.

USGS photo by J. Schmith.

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► Pillow Basalts

Pillow lavas form during subaqueous eruptions when the lava surface is rapidly quenched but the interior continues to inflate as the eruption continues. Most pillow lavas have basaltic compositions.

photo of a shoreline bluff with rounded pillow basalts exposed
Pillow basalts are present near the top of the Resurrection ophiolite in Kenai Fjords National Park, Alaska.

Photo courtesy of Cameron Davidson.

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Parks with Basaltic Lava Flows

  1. Bandelier National Monument (BAND), New Mexico—[BAND Geodiversity Atlas] [BAND Park Home] [BAND]

  2. Bering Land Bridge National Preserve (BELA), Alaska—[BELA Geodiversity Atlas] [BELA Park Home] [BELA]

  3. Big Bend National Park (BIBE), Texas—[BIBE Geodiversity Atlas] [BIBE Park Home] [BIBE]

  4. Capulin Volcano National Monument (CAVO), New Mexico—[CAVO Geodiversity Atlas] [CAVO Park Home ] [CAVO]

  5. Crater Lake National Park (CRLA), Oregon—[CRLA Geodiversity Atlas] [CRLA Park Home] [CRLA]

  6. Craters of the Moon National Monument (CRMO), Idaho—[CRMO Geodiversity Atlas] [CRMO Park Home] [CRMO]

  7. Death Valley National Park (DEVA), California & Nevada—[DEVA Geodiversity Atlas] [DEVA Park Home] [DEVA]

  8. Devils Postpile National Monument (DEPO), California—[DEPO Geodiversity Atlas] [DEPO Park Home] [DEPO]

  9. El Malpais National Monument (ELMA), New Mexico—[ELMA Geodiversity Atlas] [ELMA Park Home] [ELMA]

  10. Fort Vancouver National Historic Site (FOVA), Washington—[FOVA Geodiversity Atlas] [FOVA Park Home] [FOVA]

  11. Grand Canyon National Park (GRCA), Arizona—[GRCA Geodiversity Atlas] [GRCA Park Home] [GRCA]

  12. Grand Canyon-Parashant National Monument (PARA), Arizona—[PARA Geodiversity Atlas] [PARA Park Home] [PARA]

  13. Grand Teton National Park (GRTE), Wyoming—[GRTE Geodiversity Atlas] [GRTE Park Home] [GRTE]

  14. Hagerman Fossil Beds National Monument (HAFO), Idaho—[HAFO Geodiversity Atlas] [HAFO Park Home] [HAFO]

  15. Haleakala National Park (HALE), Hawaii—[HALE Geodiversity Atlas] [HALE Park Home] [HALE]

  16. Hawai’i Volcanoes National Park (HAVO), Hawai’i—[HAVO Geodiversity Atlas] [HAVO Park Home] [HAVO]

  17. Isle Royale National Park (ISRO), Michigan—[ISRO Geodiversity Atlas] [ISRO Park Home] [ISRO]

  18. Kalaupapa National Historical Park (KALA), Hawai’i—[KALA Geodiversity Atlas] [KALA Park Home] [KALA]

  19. Kaloko-Honokohau National Historical Park (KAHO), Hawai'i—[KAHO Geodiversity Atlas] [KAHO Park Home] [KAHO]

  20. Katmai National Park (KATM), Alaska—[KATM Geodiversity Atlas] [KATM Park Home] [KATM]

  21. Keweenaw National Historic Park (KEWE), Michigan—[KEWE Geodiversity Atlas] [KEWE Park Home] [KEWE]

  22. Lake Mead National Recreation Area (LAKE), Arizona and Nevada—[LAKE Geodiversity Atlas] [LAKE Park Home] [LAKE]

  23. Lake Roosevelt National Recreation Area (LARO), Washington—[LARO Geodiversity Atlas] [LARO Park Home] [LARO]

  24. Lassen Volcanic National Park (LAVO), California—[LAVO Geodiversity Atlas] [LAVO Park Home] [LAVO]

  25. Lava Beds National Monument (LABE), California—[LABE Geodiversity Atlas] [LABE Park Home] [LABE]

  26. Lewis and Clark National Historical Park (LEWI), Oregon and Washington—[Volcanoes of the Lewis & Clark Trail]

  27. Mojave National Preserve (MOJA), California—[MOJA Geodiversity Atlas] [MOJA Park Home] [MOJA]

  28. National Park of American Samoa (NPSA), American Samoa—[NPSA Geodiversity Atlas] [NPSA Park Home] [NPSA]

  29. Petrified Forest National Park (PEFO), Arizona—[PEFO Geodiversity Atlas] [PEFO Park Home] [PEFO]

  30. Petroglyph National Monument (PETR), New Mexico—[PETR Geodiversity Atlas] [PETR Park Home] [PETR]

  31. Pu'uhonau o Honaunau National Historic Park (PUHO), Hawai'i—[PUHO Geodiversity Atlas] [PUHO Park Home] [PUHO]

  32. Pu'ukohola Heiau National Historic Site (PUHE), Hawai'i—[PUHE Geodiversity Atlas] [PUHE Park Home] [PUHE]

  33. Rocky Mountain National Park (ROMO), Colorado—[ROMO Geodiversity Atlas] [ROMO Park Home] [ROMO]

  34. Shenandoah National Park (SHEN), Virginia—[SHEN Geodiversity Atlas] [SHEN Park Home] [SHEN]

  35. Sunset Crater Volcano National Monument (SUCR), Arizona—[SUCR Geodiversity Atlas] [SUCR Park Home] [SUCR]

  36. Voyageurs National Park (VOYA), Minnesota—[VOYA Geodiversity Atlas] [VOYA Park Home] [VOYA]

  37. Wupatki National Monument (WUPA), Arizona—[WUPA Geodiversity Atlas] [WUPA Park Home] [WUPA]

  38. Yellowstone National Park (YELL), Wyoming—[YELL Geodiversity Atlas] [YELL Park Home] [YELL]

  39. Yosemite National Park (YOSE), California—[YOSE Geodiversity Atlas] [YOSE Park Home] [YOSE]

  40. Zion National Park (ZION), Utah—[ZION Geodiversity Atlas] [ZION Park Home] [ZION]

Last updated: April 18, 2023