The Hunga Tonga-Hunga Ha’apai Eruption, a Multi-Hazard Event
Hunga Tonga-Hunga Ha’apai, located in the South Pacific Kingdom of Tonga, has erupted three times in less than thirty days. The volcano has sporadically erupted since 2009 with the most recent activity beginning in late December 2021 when a series of Surtseyan eruptions built up and reshaped the island while sending bursts of tephra and volcanic gasses spewing from the vent.
On Jan.13, 2022, NOAA’s GOES West satellite captured the second eruption. According to local officials, the eruption had a radius of 161.5 miles and sent ash, steam, and gas 12.4 miles into the air. It was more powerful than the previous eruption on Dec. 20, but an even more intense series of explosions began on January 15. The eruptions generated atmospheric shock waves, sonic booms, and tsunami waves that traveled the world and were heard as far away as Alaska.
Satellite-based lidar and limb sounder data indicated that the eruption was strong enough to send volcanic material well into the lower stratosphere (which generally begins 9 miles up in this part of the world) where, according to rawinsonde data from Fiji, easterly winds propelled the ash. Scientists watch closely when volcanic materials reach this relatively dry layer of the atmosphere because particles linger longer and travel farther than when they remain in the lower, wetter troposphere.
The plume of material created what volcanologists call an umbrella cloud with crescent-shaped bow shock waves. These also triggered a vast number of lightning strikes that were seen by the Geostationary Lightning Mapper (GLM) onboard the GOES West satellite. “The umbrella cloud was about 500 kilometers (300 miles) in diameter at its maximum extent,” said Michigan Tech volcanologist Simon Carn. “That is comparable to Pinatubo and one of the largest of the satellite era. However, the involvement of water in the Tonga eruption may have increased the explosivity compared to a purely magmatic eruption like Pinatubo.” It has been estimated that the eruption was the equivalent of around 10 megatons of TNT.
Hunga Tonga-Hunga Ha’apai first formed between Dec. 2014 and Jan. 2015, when the previously underwater volcano erupted. When all the dust, rock, and ash settled, a newly-formed island remained between two older islands, with a summit reaching 400 feet high. It was the first of its kind to form in 53 years, so scientists have been able to study its birth and evolution in vivid detail from space.
The volcano is about 40 miles north of Tonga’s main island, Tongatapu, near the international dateline. Tonga is home to 105,000 people and northeast of New Zealand and southeast of Fiji.
The blast and associated tsunami caused "significant damage" along the western coast of the main island of Tongatapu. "A thick layer of ash remains across Tongatapu," said the New Zealand High Commission in a recent statement.
At least two Tongans have lost their lives to the recent eruption, and thousands more are battling the remaining debris. One major concern is access to safe drinking water, which can be contaminated by ash and smoke from the blast.
In addition to local damage, the powerful explosion triggered large waves and tsunami advisories that reached Australia, New Zealand, Japan, and the west coasts of North and South America. Parts of Japan saw waves as high as nine feet tall, and the west coast of the United States received swells around three and four feet high. In Peru, two people died from the high water, and an oil spill was caused by the waves.
Volcanic Ash Advisory Centers (VAACs) are responsible for issuing volcanic ash advisories 24/7. VAAC forecasters use information from NOAA satellites to monitor clouds whose location, evolution and/or spectral properties are consistent with volcanic activity. The satellites can estimate the height of ash clouds, determine the extent of ash, and estimate the amount of ash present. The GOES-West GLM also imaged thousands of lightning flashes during the eruption. The advisories are also useful to air traffic controllers because large amounts of ash can significantly damage aircraft and are a major safety concern.
Given the remote location of most volcanoes and the rapid formation and expansion of volcanic clouds, geostationary satellites, like NOAA's GOES-16 and GOES-17, are the primary tool for monitoring volcanic clouds. Since they orbit 22,236 miles above Earth's equator, at the same speed Earth rotates, GOES satellites have a constant view of the same area. This means they can monitor volcanic eruptions in near real-time.
Approximately 90% of the world's volcanoes are not regularly monitored for activity. In addition, the large volumes of satellite data now available make manual examination impractical. The need to distill large amounts of data into actionable information for timely volcanic eruption detection led to the development of an automated detection tool. The VOLcanic Cloud Analysis Toolkit (VOLCAT) system automatically detects new eruptive events and issues alerts when new events occur. NOAA satellite data are critical inputs for VOLCAT.
Satellites operated by NOAA and its international partners play a crucial role in detecting volcanic activity, alerting those in harm’s way of an eruption, and monitoring the hazards associated with volcanic eruptions.
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