Nonexplosive Calderas

View of the Kīlauea caldera showing the Halemaʻumaʻu pit crater and its lava lake.

USGS photo by H. Dietterich at 10:11 a.m. HST on January 6, 2021.

Introduction

Nonexplosive calderas are found at the summit of large shield volcanoes, including Kīlauea and Mauna Loa in Hawai’i Volcanoes National Park. Unlike summit and resurgent calderas, calderas on shield volcanoes do not form during explosive eruptions. Instead they form when the summit area collapses due to the withdrawal of magma from shallow magma chambers. The magma withdrawal may occur due to flank eruptions in rift zones.

Nonexplosive calderas can form at other basaltic volcanic centers such as Twin Calderas, a long-lived vent in Bering Land Bridge National Monument that was active during the Pleistocene.

National Park Nonexplosive Calderas

At least four national parks contain nonexplosive calderas:

Bering Land Bridge National Monument

Two small calderas formed at a long-lived basaltic volcanic center between 800,000 and 900,000 years ago. These calderas have a diameter of 1,700 and 2,500 ft (520 and 760 m) and are 50 to 120 feet (15 and 36 m) deep.

Twin Calderas.

NPS photo.

Hawai’i Volcanoes National Park

Both shield volcanoes in Hawai’i Volcanoes National Park, Mauna Loa and Kīlauea, have nonexplosive calderas at their summits.

Kīlauea

The Kīlauea caldera covers an area of approximately 2.6 miles (4.2 km) by 2.0 miles (3.2 km) in dimension. The modern Kīlauea caldera collapsed about 500 years ago. Numerous calderas have existed during the volcano’s lifespan with the previous one forming about 2,200 years ago. This caldera ultimately was filled by lava flows.

The Kīlauea caldera underwent extensive collapse in 2018 during the largest eruption of Kīlauea in about 200 years. The collapse occurred when an eruption along the lower East Rift Zone partially drained the summit magma chamber which in turn caused subsidence in the caldera. The lava lake in Halemaʻumaʻu pit crater drained, and the pit crater doubled in width and increased in depth by nearly ten times.

The Kīlauea summit caldera before and after its collapse in 2018.

USGS photo.

Featured Links

• Hawaiʻi Volcanoes—2018 Eruption and Summit Collapse

• Hawaiʻi Volcanoes—2020-2021 Summit Eruption

• NPS—Three Big Changes in Three Years at Halemaʻumaʻu Crater

• USGS—Kīlauea Volcano Erupts in Explosive and Effusive Cycles

Mauna Loa

Moku‘āweoweo, Mauna Loa’s caldera, is about 4 miles (6.2 km) long by 1.5 mi (2.5 km) wide, consisting of three oval depressions and is located at the summit above 12,000 feet (3,660 m) in elevation. Mauna Loa has had several calderas during its history that were filled in by later eruptions, with this caldera forming between 1,000 and 1,500 years ago. It formed during a large eruption on the northeast rift zone that produced the Pana`ewa lava flow that covers an area of 66 square miles (172 square km) with a maximum thickness of more than 33 ft (10 m).

Moku‘āweoweo. Photo taken in 2009.

USGS photo by Ben Gaddis.

National Park of American Samoa

American Samoa is made up of eroded Pleistocene-age shield volcanoes.

Pago Pago Harbor is located in the caldera of the Pago Shield Volcano on Tutuila Island. The volcano erupted about 1.27 million years ago. The harbor is on the border of National Park of America Samoa.

NPS photo.

Wrangell-St. Elias National Park and Preserve

Several of the andesite shield volcanoes in Wrangell-St. Elias National Park contain nonexplosive calderas.

The ice-filled caldera of Mount Wrangell.

USGS Photo by R. J. Motyka, Alaska Volcano Observatory, 1987.

Overall Description

Nonexplosive calderas are typically steep-sided and may have relatively flat floors due to filling with lava flows or lava lakes. They may also contain smaller collapse structures known as pit craters.

Magma Composition

Lavas of basalt to andesite composition are typically erupted in nonexplosive calderas. This is also true of shield volcanoes where nonexplosive calderas occur.

Eruption Styles

Most eruptions in nonexplosive calderas are effusive, usually 0-1 on the Volcanic Explosivity Index (VEI), typically in the Hawaiian eruptive style. These eruptions produce fluid lava flows and may produce fire-fountains.

Features

Pit Craters

Pit craters are small craters formed from subsidence or collapse. They may be present within nonexplosive calderas at the summit of shield volcanoes, such as Halemaʻumaʻu in the Kīlauea caldera.

The Halema'uma'u pit crater containing an active lava lake on December 13, 2021.

USGS photo by J.M. Chang.

Lava Lakes

Lakes or molten or solidified lava may be present in summit calderas of shield volcanoes. Lava lakes may form when there is open connectivity between the vent and the subsurface magma chamber.

Learn More

• NPS—Lava Lakes

Fumaroles

Fumaroles in nonexplosive calderas indicate where heat and magmatic or meteoric gases are escaping. Fumaroles are also present when there is molten lava present.

Learn More

• NPS—Funaroles (Article)

Thermal map of Kīlauea caldera on April 8, 2019 nearly a year after the 2018 collapse. Fumaroles exist in the Halema‘uma‘u pit crater and along fractures where collapse occurred.

Occurrence

Nonexplosive calderas are usually located at the summit of large shield volcanoes, but they may occur in other basaltic volcanic centers.

Volcanic Hazards

Vog (volcanic smog) consists of SO2 (sulfur dioxide) gas and aerosols produced by eruptions or gas emissions in nonexplosive calderas. It presents a hazard both in the immediate area and to people who are downwind.

Rock falls, subsidence, and active fumaroles may also present volcanic hazards.

Learn More

Be Geohazard Aware

National Park Sites containing Nonexplosive Calderas

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

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

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

• Wrangell-St. Elias National Park and Preserve (WRST), Alaska—[WRST Geodiversity Atlas] [WRST Park Home] [WRST npshistory.com]

Volcanoes, Craters, and Lava Flows