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Volcano Watch: How Does HVO Determine Regions Most Threatened by Lava Flows? – Honolulu, Hawaii

Honolulu, Hawaii 2021-09-21 23:52:19 –

An aerial view of the Hawaiian Volcano Observatory helicopter of the lava channel from crevice 8 during the 2018 lower east rift zone eruption of Kilauea. All 24 cracks from this eruption occurred within Lava Flow Hazard Zone 1, the area with the highest lava flow coverage. Lava flows erupted from these crevices covering 13.7 square miles and destroyed more than 700 homes. All of these are in lava flow hazard zones 1 and 2. The cone in crevice 8 is hidden by a cloud of steam (upper center). A USGS photo taken on July 10, 2018.

Most inhabitants of the Big Island live in one of four active volcanoes and may have wondered about the threat of lava flows.

Interestingly, past knowledge is needed to determine future threats. The potential for a region to be invaded by lava in the future is estimated in two different ways based on the history of lava flow activity.

One approach uses a geological map to calculate the amount of lava-covered surface over various periods dating back to the past. The resulting number is called the coverage rate. Another approach is to calculate how often lava flows occur within a particular area over time. The resulting number is the probability of lava flow.

NS 1992 Lava Flow Hazard Zone (LFHZ) Map Represents the use of a long-term coverage rate-based approach. It does not indicate how fast an individual lava flow travels, but the rate at which lava covers areas of multiple eruptions over the centuries. For example, more than a quarter of Kilauea volcano has been covered since the Hawaiians hosted the British Captain Cook who visited the island, and nearly 90 of the volcanoes since the arrival of the Polynesians about 800-1,000 years ago. % Was covered. An assessment of future activity using these coverages estimates that the majority of volcanoes will resurface with new lava within the next 1,000 years.

The new eruption covers not only the old flow but also some of the latest lava, so the coverage rate is not significantly affected. For example, 2018 lava flowed during and above some of the 1790, 1955, and 1960 lava flows. Therefore, “coverage” or resurfacing since 1790 did not increase in all areas of the 2018 flow, but only in the areas beyond the previous flow.

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The 1992 LFHZ map shows that the highest coverage (and therefore dangerous) is at the rift zones and summits of Kilauea and Mauna Loa volcanoes. Since 1790, almost half of both volcanoes’ LFHZ 1 (the most dangerous zone) have been covered. Coverage decreases as you move away from LFHZ1.

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Another approach to estimating the risk of long-term lava flow is to calculate how often a particular area is affected by lava. This is also known as the recurrence interval method. Kilauea’s Lower East Rift Zone (LERZ) has been covered with lava five times since 1790, 1790, 1840, 1955, 1960 and 2018. These eruptions have occurred for over 200 years, averaging about 60 years. Between them.

The recurrence interval method is the most widely used in flood hazard calculations and traditionally creates hazard maps based on an average 100-year recurrence interval between damaging floods. Using the simplest formula of probability (French mathematician Denis Poisson), its recurrence interval is 1% likely to damage floods that occur in any year, 39. Will be%. Surprisingly, the probability of such a flood occurring in the first century is 63% (about 3 to 2) instead of 100%. This is because the recurrence interval is the average of the actual intervals and can vary considerably.

For lava flow applications, an average recurrence interval in LERX of about 60 years means a 63% chance of another lava-free recurrence interval of 60 years (3 to 2 probability again). It means that. It is also possible that another lava flow will affect some of the LERX within 60 years. The probability of lava flow in the region for 30 years is 40% or 2 to 3 odds, and the probability of flooding is 26% (1 to 3 odds). Fortunately, the combined areas of LERZ lava and flood hazards are limited as follows: Coastal flood zone..

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Lava flow hazard calculations and maps produced by the United States Geological Survey (USGS) aim to inform real estate owners, emergency managers, and government planners of long-term hazards caused by lava flows. It is said. The USGS Hawaiian Volcano Observatory continues to investigate the dangers of lava flows using these and other methods.

For more information on lava flow risk probabilities, the following publications are available:

Update of volcanic activity

Kilauea is not erupting. Its USGS Volcanic Alert Level is at ADVISORY.

Kilauea update Published weekly.

Kilauea volcano has not erupted. After a recent invasion of magma beneath the surface of the area south of Kilauea Caldera and a significant slowdown on August 30, seismic rates and ground movements in this area have remained close to pre-invasion levels. Other surveillance data streams, such as sulfur dioxide emission rates and webcam displays, do not show significant changes.

For more information on Kilauea’s current monitoring, see. https://www.usgs.gov/volcanoes/kilauea/monitoring.

Mauna Loa has not erupted and remains a volcanic alert level recommendation. This alert level does not mean that the eruption is imminent or that the progress from the current level of anxiety to the eruption is certain. The latest information on Mauna Loa Published weekly.

Last week, a small magnitude earthquake of about 66 was recorded under the elevation sides of the summit and top of Mauna Loa. Most of these occurred at shallow depths of less than 8 km (5 miles). Global Positioning System (GPS) measurements have not seen significant changes in the past week. Gas concentrations and fumarolic temperatures remain stable at both the summit and the sulfur cones in the southwestern rift zone. The webcam shows no change in the landscape. For more information on Mauna Loa’s current surveillance, see: https://www.usgs.gov/volcanoes/mauna-loa/monitoring..

Last week there were three events in the Hawaiian Islands, including three or more felt reports.

  • September 15 at 7:36 am HST M3.2 earthquake at a depth of 32 km (20 miles) 2 km (1 mile) southwest of Pahara
  • September 15 3:09 am HST M2.6 earthquake 5 km (3 miles) west-southwest of Kealakekua at a depth of 4 km (2 miles)
  • September 12, 1:45 am HST at 36 km (22 mi) depth Pahara’s ENE 6 km (3 mi) M3.8 earthquake

HVO continues to closely monitor both Kilauea and Mauna Loa for signs of increased activity.

visit HVO website Past volcano watch articles, Kilauea and Mauna Loa updates, volcano photos, maps, recent earthquake information and more.

Email your question [email protected]..

Volcano Watch is a weekly update of articles and activities written by scientists and affiliates of the US Geological Survey Hawaiian Volcano Observatory.



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