Beyond the lava: Mauna Loa's Deformation Story — USGS Volcano Watch

Mauna Loa volcano stands as the largest and most active volcano on Earth. With a rich history of eruptions that have shaped the Island of Hawaʻi's geography, Mauna Loa has captivated the fascination of scientists, residents, and people worldwide. Let's take a closer look at how Mauna Loa’s surface deformation has changed over the last several decades, focusing on its three most recent eruptions.

By comparing data from past eruptions, scientists gain valuable insights into a volcano's patterns and cycles. This knowledge helps us better understand a volcano's behavior, preparing us for future unrest and allowing us to communicate potential hazards to nearby communities. 

Global Positioning System (GPS), borehole tiltmeters, Interferometric Synthetic Aperture Radar (InSAR), and seismometers are currently the primary geophysical instruments for measuring changes and unrest at volcanoes. These have replaced older, less advanced surveying instruments that were used in the past. 

The most recent Mauna Loa eruptions in 1975, 1984, and 2022 each offer unique insights into this volcano’s eruptive behavior. 

In 1975, lava suddenly flowed from Mauna Loa’s summit, creating a mesmerizing sight. The eruption lasted less than a day. Although brief, it left its mark on the landscape, reminding us of the volcano's power and unpredictability. Prior to the 1975 eruption, Mauna Loa showed slight extension across the summit caldera in 1974, indicating inflation. There was also an uptick in seismic activity beforehand. After the 1975 eruption, Mauna Loa inflated by about 8 inches (20 centimeters) across its caldera between 1975 and 1976.

Nine years later, Mauna Loa came to life again. This time, there was almost a year of clues indicating an eruption could be coming. Some of these included elevated rates of ground inflation and increased numbers of earthquakes. USGS Hawaiian Volcano Observatory (HVO) scientists were able to detect changes in the volcano and were able to communicate to the public that there was a high likelihood for an eruption. 

In March 1984, the volcano erupted with renewed vigor. This time, the eruption lasted longer, spewing lava for 22 days. The lava flowed from the summit, creeping down the northeast flank of the volcano from fissures on the volcano's Northeast Rift Zone. As lava was erupted on the surface of the volcano, it deflated. Then, after the eruption stopped, Mauna Loa reinflated for more than a year and a half.

Following decades of quiet, Mauna Loa stirred from its slumber once again in 2022. With increased seismic activity beneath its summit and notable surface deformation starting in September 2022, Mauna Loa signaled its awakening. HVO scientists worked with the Hawaii County Civil Defense Agency to inform communities about the potential for an eruption. On November 27, 2022, lava began to flow—first in the caldera, to the south caldera, and then to the Northeast Rift Zone. The eruption lasted for two weeks, captivating the world with its awe-inspiring display of molten lava flows. 

Following all three eruptions, reinflation was very fast right after lava effusion ended but gradually waned over the following years. Maybe more interesting are the differences in Mauna Loa’s detectable behavior before each of these eruptions. There were small changes in ground deformation and many earthquakes before the 1975 summit eruption, whereas the 1984 and 2022 eruptions were proceeded by many earthquakes and major ground deformation.

It's possible that small and short-lived Mauna Loa summit eruptions like 1975 may not show as intense precursors compared to larger, longer eruptions with rift-zone activity. It’s also possible that the differences in technology, improved instrumentation, and data collection techniques between the 1970s and today contributed to the improved detection of volcano deformation in 2022 compared to previous eruptions. 

As Mauna Loa slumbers once more, HVO scientists continue to monitor the volcano with advanced technology, refining our understanding of its behavior and enhancing early warning systems. Ground deformation prior to and after recent Mauna Loa eruptions have provided us with insights into the patterns of behavior, and we will only learn more during future unrest and eruptions.

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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. 

mages and captions from USGS: HVO scientist setting up temporary GPS equipment south of Kaluapele (the summit caldera of Kīlauea volcano).The long profile of Mauna Loa volcano is prominent in the background. USGS image by D.A. Phillips.