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| Hawaiian Volcano Observatory geologists and a National Park Service archaeologist hike west along the Hilina Pali Trail on July 26, 2023. USGS photo by D. Downs |
SEARCHING FOR TEPHRA from one of Kīlauea's largest explosive eruptions is the subject of this week's Volcano Watch, written by U.S.G.S. Hawaiian Volcano Observatory scientists and affiliates.
This week's article was written by HVO geologist Kendra J. Lynn.
Understanding the eruptive history of volcanoes in Hawai‘i requires a tremendous amount of time and effort in examining deposits. Typically, older eruptions have less material exposed at the surface because younger eruptions bury them, or wind and rain erode them. Such is the case for one of Kīlauea's largest explosive eruptions, which is not exposed near its source at the summit and must be studied further afield.
Although Kīlauea is world-renowned for its lava flow eruptions, it also has a history of explosive eruptions. The two most recent explosive periods, which created deposits named the Uwēkahuna Ash and Keanakāko'i Tephra, were preceded by huge outpourings of lava. These large lava flow eruptions may have drained Kīlauea's summit plumbing system and caused caldera collapse; subsequent activity was explosive.
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| Tephra comes in many forms including these rock fragments, tiny spheres and shards of volcanic gas. USGS photo |
The older Uwēkahuna Ash represents possibly 1,200 years of dominantly explosive activity, yet only a few detailed geologic studies exist for these deposits. The type locality of Uwēkahuna Ash was a vertical section within the Uēkahuna bluff on the western wall of Kaluapele (Kīlauea's summit caldera), but summit collapses in 2018 and subsequent rock falls buried this location. Fortunately, we can study samples that were collected from this location and collect new samples from the same deposits further away from the summit.
The Kulanaokuaiki Tephra is a subset of the Uwēkahuna Ash. It erupted between 400–1000 CE. HVO geologists and collaborators are focusing on one part of this deposit—named Kulanaokuaiki-3 (K-3, for short)—because it is one of the largest known explosive eruptions at Kīlauea in the past several thousand years.
K-3 explosive activity likely had an eruption column that reached 14–18 km (9–10 miles) above sea level for several hours. The K-3 plume dispersed tephra, in a southeast direction, across an area larger than 65 square km (16,000 acres), from Kīlauea's summit all the way to Halapē on the coastline 17 km (10.5 miles) away.
Recently, HVO scientists conducted fieldwork in the backcountry of Hawai‘i Volcanoes National Park They focused on finding, measuring, and sampling deposits from K-3 to better understand how, when, and why eruptions of this magnitude might occur. This work was conducted under the supervision of an HAVO archaeologist, who ensured our work would not disrupt any cultural or natural resources.
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| Volcanic ash from Kīlauea Volcano is tephra. USGS photo |
In the field, HVO geologists dug small pits in soil and tephra that have accumulated in the low spots on the lava flows that cover the surface of Kīlauea's south flank. Once exposed, the layers of soil, ash, and tephra within the pits were measured, described, and sampled.
Using these samples we'll assess the degree of tephra fragmentation—a proxy for eruption intensity and size—by measuring the shape and size distribution of tephra grains using state-of-the-art analytical equipment in the HVO Tephra Lab. Magma degassing during the eruption will be evaluated by measuring tephra density using a high-precision pycnometer and/or 3D scanner in the HVO Tephra Lab. Using microscopes, we'll investigate how much of the sample is fresh versus recycled older lava. These physical parameters will help us to understand the K-3 deposit and the eruptions that created it.
Kīlauea has not had an explosive eruption as large as the K-3 in modern times. It's important to evaluate what generates such large eruptions because a similar eruption today would be devastating to communities surrounding Kīlauea summit and downwind. Another K-3-sized eruption would likely inject volcanic ash into the subtropical jet stream and disrupt regional air traffic.
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| Tephra deposits at Kilauea and go back to the year 1500 in just these deposits. USGS photo |
Volcano Activity Updates:
Kīlauea is not erupting. Its USGS Volcano Alert level is ADVISORY.
Active lava has not been visible within Halemaʻumaʻu crater at the summit of Kīlauea since June 19. Earthquake activity in the summit region remained slightly increased over the past week. Summit tiltmeters generally showed inflation over the past week. A sulfur dioxide (SO2) emission rate of approximately 120 tonnes per day was measured on August 6.
Mauna Loa is not erupting. Its USGS Volcano Alert Level is at NORMAL.
Webcams show no signs of activity on Mauna Loa. Seismicity remains low. Summit ground deformation rates indicate slow inflation as magma replenishes the reservoir system following the recent eruption. SO2 emission rates are at background levels.
There were three earthquakes with three or more felt reports in the Hawaiian Islands during the past week: a M3.2 earthquake 4 km (2 mi) S of Volcano at 2 km (1 mi) depth on August 9 at 10:40 a.m. HST, a M3.6 earthquake 4 km (2 mi) NNE of Wai‘ōhinu at 12 km (7 mi) depth on August 4 at 8:30 p.m. HST, and a M3.9 earthquake 69 km (42 mi) WNW of Kalaoa at 43 km (26 mi) depth on August 4 at 5:24 a.m. HST.
HVO continues to closely monitor Kīlauea and Mauna Loa.
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| FEMA brought in a recovery crew including cadaver dogs. Photo from Governor's Office |
TO BETTER PREPARE FOR FUTURE WILDFIRES AND TO BETTER UNDERSTAND decisions made before and during this week's Maui and Hawai‘i Island wildfires, is the aim of Hawai‘i's Attorney General Anne Lopez. She announced on Friday that the Department of the Attorney General will conduct "a comprehensive review of critical decision-making and standing policies leading up to, during, and after the wildfires on Maui and Hawaiʻi islands."
Lopez said, “The Department of the Attorney General shares the grief felt by all in Hawaiʻi, and our hearts go out to everyone affected by this tragedy. She said her Department is committed to "sharing with the public the results of this review. As we continue to support all aspects of the ongoing relief effort, now is the time to begin this process of understanding."
The death rate climbed to 89 on Saturday, with the arrival of 8 cadaver dogs with 12 more to come, to go through the charred buildings and ruins of cars and other sites. In a press conference, Maui Police Chief John Pelletier called again for patience. He said that only 3 percent of the structures have been checked for remains and given that many are burnt to the ground, identifying them is extremely difficult. He recommends that those with relatives who are missing have their DNA tested so an information bank can be established to match remains with relatives. He talked about the pono way of proceeding with respect, aloha and dignity, "because we are Hawai‘i and we are Maui." Referring to the remains of people on the ground, he called for moving slowly since "We are walking on it." He called for "patience, prayers, perseverance." Only a handful of remains have been identified.
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| AG Anne Lopez will conduct a review on decision-making regarding the wildfires. |
Kaʻū's member of Congress, Jill Tokuda, who also represents Maui and all rural Hawai‘i, praised "all the frontliners." Public officials noted that on the ground there are 50 members of the National Guard, 150 representing FEMA, and the Coast Guard, which saved 17 lives and assisted locals in saving 40 more when people fled to the ocean to escape the fire. In addition the military is helping with helicopters and other assets.
Gov. Josh Green, who called Lahaina "Ground Zero," said that one goal is to get displaced survivors into housing as soon as possible and reported that 1,000 hotel rooms on Maui will be used. Five hundred will be for the displaced and 500 for those who have come in to help out, including FEMA, CDC and SBA. He said that 15,000 people, mostly visitors who were on the island, have left. Next is working on long-term housing, said the Governor. The Coast Guard representative said that "We understand that Lahaina Harbor is the lifeblood of Lahaina" and promised to help make it operable as soon as possible.
Tokuda, who visited Lahaina on Saturday, said that while one of her favorite historic places, Lahaina Library is gone, its wooden sign remains untouched, giving her hope for Lahaina's future.
FEMA Administrator Deanne Criswell also visited Lahaina noted that since 2018 the agency has maintained five times the amount of commodities it stores in Hawai‘i for emergencies.
To read comments, add your own, and like this story, see facebook.com/kaucalendar. See latest print edition at kaucalendar.com, in the mail and on stands.
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