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Questions about volcanic ash and other tephra from Kīlauea

Color image showing a pile of brown ash particles on a white background
Volcanic ash erupted on March 24, 2008, Halema‘uma‘u Crater, Kīlauea Volcano, Hawai‘i. (Public domain.)

1. What is volcanic ash?

Volcanic ash is a term for fine-grained material that is ejected during explosive volcanic eruptions. Volcanic ash particles are smaller than 2 mm (0.08 inches) in diameter. Volcanologists use the word ‘tephra’ as general term for volcanic rock fragments irrespective of grain size produced during an explosive eruption. Volcanic ash is fine tephra, and terms such as lapilli, blocks, and bombs are used to categorize larger fragments. Such larger fragments are relatively heavy and fall near the vent, and it is generally volcanic ash that can be carried great distances by wind, traveling far enough to impact society.

A number of processes can cause explosive eruptions and hence produce volcanic ash and other tephra. Ejected particles can be derived directly from magma or from breakage of solid rocks. All explosions are driven by pressurized gas, either coming from the magma itself, from heated groundwater or surface water, or both. Rapid expansion of gas upon eruption breaks magma or solid rock into particles, producing tephra.

Color photograph of black volcanic tephra on a white table
Tephra, including rock fragments, tiny spheres, and shards of volcanic glass, that was erupted from Halema‘uma‘u Crater, Kīlauea Volcano, Hawai‘i. (Public domain.)

Volcanic ash is not the product of combustion, like the soft, fluffy material created by burning wood, leaves, or paper. Volcanic ash is hard and does not dissolve in water. The term "ash" comes from a time when people thought that magma was fire. We know better now! It is also extremely abrasive and mildly corrosive.

The volcanic ash produced by small explosions at Halema‘uma‘u Crater's Overlook vent in 2008-2018 is a mixture of lithic fragments (pulverized rock) and tiny spheres and shards of volcanic glass, including Pele's hair and Pele's tears.

2. When has Kīlauea erupted volcanic ash?

Color photograph showing an exposure of tan to grey volcanic tephra deposits
Tephra deposits as thick as 11 m (36 ft) at summit of Kīlauea Volcano, Hawai‘i, were erupted during an extended period that included many explosive eruptions between about 1500 and the early 1800s. (Public domain.)

Kīlauea Volcano is known for its relatively benign eruptions of fluid lava flows. Therefore, many people were surprised by the small explosions that occurred in Halema‘uma‘u Crater in March and April 2008. However, ash emissions from Halema‘uma‘u Crater and elswhere at the summit of Kīlauea are not unknown in the volcano's history.

Kīlauea's summit has erupted explosively throughout the history of the volcano, producing tephra deposits that date back at least 30,000 years and probably older. For more than 300 years starting in about 1500 CE, repeated explosions deposited tephra around the summit accumulating to more than 11 m (36 ft) in thickness. In 1790, near the end of this explosive period, at least 80 people were killed in the summit region by searing hot gas and ash produced by a devastating explosion. More recently, in 1924, more than 50 explosions in Halema‘uma‘u Crater blasted columns of tephra, mostly volcanic ash, as 3 km (2 mi) into the air. Ash plumes were blown downwind beyond the community of Pahala, 32 km (20 miles) away. Muddy ash also fell in lower Puna, making railroad tracks too slippery for train travel in Maku‘u. One person was killed near Halema‘uma‘u when he ventured too close to the vent and was hit by falling rocks.

3. Who monitors ashfall from Kīlauea?

Color photograph of a person in an orange shirt and a yellow hard hat collecting brown volcanic ash particles from a wooden box
HVO geologist collects ash downwind of Halema‘uma‘u Crater, Kīlauea Volcano, Hawai‘i. (Public domain.)

During the 2008-2018 Kīlauea summit eruption and during the 2018 Kīlauea summit collapse events, USGS HVO scientists collected ashy daily from downwind of Halema‘uma‘u that had fallen during the past 24 hours. HVO scientists collected tephra when it was being produced during the onset of Kīlauea's current eruption. The samples are taken back to HVO, where it is weighed to calculate average accumulation rate. It is also inspected under a microscope to determine composition - lithic fragments (pulverized old rocks), volcanic glass (juvenile material), or a combination of both. The glass component of the ash is then sent for chemical and petrographic analyses. HVO scientists continue to conduct research on ash deposits in the Kīlauea summit region.

4. How much ash is Kīlauea currently erupting?

Color photograph showing a greyish brown ash plume rising from a crater vent
View of ash-rich plume rising from a new vent in Halemaʻumaʻu Crater in Kīlauea Caldera 5 days after the first explosion from the vent occurred on March 19, 2008. The ash is turning the formerly white steam and gas plume a dusty-brown color. Note the ash fallout downwind of the plume. Earlier in the day, geologists reported finding Pele's hair, Pele's tears, and spatter on the rim of Halemaʻumaʻu, indicating that particles ejected overnight included molten lava. This is the first lava to erupt from the new vent, which was 30-35 m (100 ft) wide. The largest fragments of spatter, or blobs of molten rock, found on the crater rim were 10 cm (4 inches) in size. (Public domain.)

Kīlauea is not currently erupting ash. The highest rate of ash deposition during the 2008-2018 Kīlauea summit eruption occurred on March 19, 2008, when the new vent opened on the floor of Halema‘uma‘u Crater. The second more voluminous explosion occurred on the last day that the lava lake was visible, May 9, 2018. 

Volcanic ash and Pele's hair falling from the small Halema‘uma‘u explosions during the 2008-2018 summit eruption occasionally reached areas beyond the boundaries of Hawai‘i Volcanoes National Park, particularly during Kona wind conditions.

5. Does volcanic ash pose hazards to human health?

Like airborne particles from dust storms, forest fires, and air pollution, volcanic ash particles are often small enough (less than 10 microns) to be inhaled deeply into the lungs. Thus, volcanic ash poses a health risk, especially to children, elderly people, and individuals with cardiac or respiratory ailments, such as asthma, chronic bronchitis, and emphysema.

6. What other hazards are associated with volcanic ash?

Heavy ash fall can collapse roofs, cause short circuits and damage in electronic components, interrupt telephone and radio communications, cause power outages, clog air filters in vehicles and machinery, create poor visibility, make roads slippery or impassable, damage crops, and cause harm to grazing livestock.

Airborne volcanic ash poses a serious hazard to aviation because it can diminish visibility, damage flight control systems, and cause jet engines to fail. The greatest danger is to aircraft near the source of the ash cloud, but winds can blow volcanic ash great distances, so it can also pose a hazard to aircraft far downwind of an erupting volcano.

Due to the 2008–2018 Kīlauea summit eruption, concerns about explosions from Halema‘uma‘u led the Federal Aviation Administration to close the airspace at or below 5,000 feet above ground level and three nautical miles from Halema‘uma‘u Crater to minimize risks to aircraft flying near the summit of Kīlauea.

7. What can I do to minimize the impacts of volcanic ash?

As with any natural disaster, communities and homeowners should develop an emergency-response plan that can be activated if Kīlauea erupts large amounts of volcanic ash. Having a plan in place before an eruption occurs can greatly reduce the harmful and disruptive effects of ash.

Heavy ash fall is not currently expected from Kīlauea, but even small amounts of ash can be problematic to humans, animals, and plants. Web sites listed below provide helpful suggestions on how to prepare for, and contend with, ash fallout.