Hawaii Volcano Blog

Spaceborne Sentinel Keeps Watch Over Hawaiian Volcanoes

August 6, 2021, 6:30 AM HST
* Updated August 6, 5:35 AM
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Volcano Watch is a weekly article and activity update written by U.S. Geological Survey Hawaiian Volcano Observatory scientists and affiliates.

Geologists at the USGS Hawaiian Volcano Observatory (HVO) had their mobile phones buzzing this past week with automated alert messages, notifying them that there was something new and hot on the Island of Hawaiʻi. Although the internal alert system is meant to detect new volcanic activity, no eruption was occurring.

One of the first images collected by GOES-17 upon its arrival in orbit, before shifting to its permanent position at 137° west longitude. Image from May 20, 2018. Courtesy NOAA-NASA.
(Public domain.)

Instead, the alert was triggered by an image of the recent large brush fire on the west side of Mauna Kea. The image that captured this activity doesn’t just cover the Island of Hawaiʻi—it encompasses much of the Pacific region.

What could possibly have such a broad view of the Earth? The answer: a geostationary satellite, orbiting 22,000 miles (35,000 km) above Earth’s surface.

The image originated from a Geostationary Operational Environmental Satellite (GOES-17), operated by the National Oceanic and Atmospheric Administration (NOAA). GOES-17, launched in 2018, is a relatively new edition in a series of GOES satellites that date back to 1975, when GOES-1 launched.


Many imaging satellites are polar orbiting, staying closer to Earth’s surface in a low orbit. They image the Earth like you might mow a lawn—in narrow, sequential strips as the satellite traverses from pole to pole.


Geostationary satellites like GOES, however, have orbits that hover over a single spot on the Earth. This requires being much farther from Earth than polar orbits, but it has the benefit that the satellite can “see” the entire side of the planet in one view.

The United States uses two GOES satellites to cover the whole country. GOES-16 (also called GOES-East) hovers over longitude 75° West (near the east coast), viewing the mainland and much of the Atlantic Ocean. GOES-17 (GOES-West) is over longitude 137° West (close to halfway between Hawaii and the mainland) and views the western U.S. and much of the Pacific Ocean.

The primary mission of GOES satellites isn’t to detect volcanic activity or forest fires, but to keep a constant watch over the weather. The broad view allows scientists to track weather systems as they evolve and migrate, providing critical data for forecasts.

A GOES infrared image of the Island of Hawaiʻi from July 31, 2021.  The warmer color region in the northern portion of the island is the recent brush fire. 
(Public domain.)

Weather monitoring uses wavelengths of visible and infrared light to characterize the atmosphere. Fortunately, the satellite infrared channels can also pick up hot thermal signals on the ground, such as those from fires and eruptions.

The geostationary nature of GOES-17 allows it to image areas rapidly—every 5–15 minutes —providing a timely view of what’s happening on this side of the planet. The satellite also has a mode to image smaller areas of Earth’s surface at even higher rates (every 30 seconds), by request in special cases, such as during a volcanic eruption or large fires. Polar-orbiting satellites, on the other hand, might only cover a given spot on the Earth twice a day.

The drawback of the distant geostationary orbit of GOES, however, is that the resolution of the images is generally lower than that of polar-orbiting satellites. The infrared channels on GOES-17 have a resolution of 2 km (1.2 miles), an improvement over its predecessor, GOES-15, which had a resolution of 4 km (2.5 miles).

The lower resolution means that GOES images aren’t adequate to map out the precise outline of a lava flow, or locate the exact location of a vent. However, the high image frequency provided by GOES is ideal for detecting the onset of new volcanic activity on the surface, while giving a general idea of where that activity is located (for example, a volcano’s summit region, or lower rift zone).

Think of GOES as a warning bell to mobilize the forces, adding to the suite of other monitoring tools used by volcano observatories to detect eruptions. While seismic and ground-deformation networks are sensitive to changes below the surface, the GOES satellite is a tool for spotting new lava reaching the surface.

The GOES satellite acts as a high-tech sentinel, maintaining an unwavering watch for eruptive activity, not only in Hawaii, but across the U.S.

GOES images and raw data are all publicly available online, just minutes after acquisition. One online interface is provided by NOAA: https://www.star.nesdis.noaa.gov/GOES/index.php.

HVO is still refining its alarming and use of GOES data, with the hope that it will help in the next eruption onset. With a history that “goes” back to 1975, it’s likely that GOES satellites will remain on watch duty for many years to come.

Volcano Activity Updates

Kīlauea is not erupting. Its USGS Volcano Alert level is at ADVISORY (https://www.usgs.gov/natural-hazards/volcano-hazards/about-alert-levels). Kīlauea updates are issued weekly.

No surface activity at Kīlauea Volcano has been observed by field crews or webcam images since May 23, 2021. Seismicity has slowly increased in recent weeks in the summit region, with continued gradual summit inflation over the past several months and no deflation-inflation cycles over the past week. Sulfur dioxide emission rates remain slightly elevated. It is possible that the Halema‘uma‘u vent could resume eruption or that Kīlauea is entering a longer period of quiescence prior to the next eruption. For more information on current monitoring of Kīlauea, see https://www.usgs.gov/volcanoes/kilauea/monitoring.

Mauna Loa is not erupting and remains at Volcano Alert Level ADVISORY. This alert level does not mean that an eruption is imminent or that progression to an eruption from the current level of unrest is certain. Mauna Loa updates are issued weekly.

This past week, about 39 small-magnitude earthquakes were recorded below Mauna Loa. Global Positioning System (GPS) measurements show no major deformation in the summit region over the past week. Gas concentrations and fumarole temperatures at both the summit and at Sulphur Cone on the Southwest Rift Zone remain stable. Webcams show no changes to the landscape. For more information on current monitoring of Mauna Loa, see: https://www.usgs.gov/volcanoes/mauna-loa/monitoring.

There were 3 events with 3 or more felt reports in the Hawaiian Islands during the past week. a M2.7 earthquake 2 km (1 mi) W of Honaunau-Napoopoo at 8 km (5 mi) depth on July 31 at 8:12 p.m. HST, a M2.7 earthquake 10 km (6 mi) SSE of Pa‘auilo at 8 km (5 mi) depth on July 30 at 2:06 a.m. HST, and a M3.2 earthquake 14 km (8 mi) S of Fern Forest at 6 km (3 mi) depth occurred on July 29 at 10:48 p.m. HST.

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

Visit HVO’s website for past Volcano Watch articles, Kīlauea and Mauna Loa updates, volcano photos, maps, recent earthquake info, and more. Email questions to [email protected].

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