Volcano Watch – Explosive eruptions from Kīlauea: beneficial or dangerous depending on location

Volcano Watch is a weekly article and activity update written by U.S. Geological Survey Hawaiian Volcano Observatory scientists and affiliates.

Twenty-five years ago, the frequently explosive activity of Kīlauea was unappreciated. Since then, continuing research has emphasized Kīlauea’s past, and potential future, explosive eruptions.

Many such explosions resulted from the interaction of magma with groundwater or surface water; others apparently were powered by pressurized gas possibly aided by steam but with no direct involvement of magma.

Lava fountains that accompany eruption of lava flows are technically explosive but are less powerful. They rarely eject particles of lava more than a few hundred meters above the vent, whereas the more powerful explosions send volcanic ash several kilometers into the air.

The powerful explosive eruptions were particularly frequent at Kīlauea during two long periods of time, from about 200 BCE (Before Common Era) to 1000 CE (Common Era) and about 1500 CE to the early 1800s.

Most past explosive eruptions took place when a deep caldera indented the summit of Kīlauea. This is where the explosive deposits are thickest and societal impacts the greatest. This is apparent when driving between Kīlauea Military Camp and Uēkahuna Bluff in Hawai´i Volcanoes National Park. Few outcrops of lava flows occur along the way, because the flows are covered by tephra deposits from explosive eruptions between 1500 and 1790 CE. And, several hundred people were killed nearby during the infamous explosive eruption in 1790. The prospect of future explosions is understandably and rightfully worrying.

But explosive eruptions are not bad everywhere. Hawaiian society southeast of Kīlauea’s summit actually benefited from some of them. These benefits result from the deposits of fine volcanic ash that transformed a barren sea of pāhoehoe into an area capable of sustaining agriculture.

One example is in Kīpukakahaliʻi, along the Chain of Craters Road south of Maunaulu. About a thousand feet (a few hundred meters) east of the vehicle pullout is a grove of more than 20 ki plants, some 7-10 feet (2-3 meters) tall. The ki grow on a flat and adjoining hill that together form a kīpuka covered with deposits of volcanic ash 10-12 inches (25-30 centimeters) thick from several explosive eruptions between about 600 and 900 CE. The top of the deposit formed the ground surface for hundreds of years and developed a soil in which the ki thrives.

Sugar cane grew there, too. Rev. William Ellis describes his guide supplying him with refreshing cane from the kīpuka during his epic walk from the summit of Kīlauea to Kealakomo on August 2, 1823. The accompanying map shows the locations and times along his journey, interpreted from his published journal.

The village of Kealakomo, near the coast south of Kīpukakahaliʻi, likewise benefited by its location astride two kīpuka containing volcanic ash deposits of the same age as those in Kīpukakahaliʻi. The deposits are thinner than those in Kīpukakahaliʻi, because they are farther downwind from the caldera, but they nonetheless provided a suitable substrate for the growth of sweet potatoes and possibly other vegetables. The village probably depended on these crops to augment its seafood diet.

Perhaps the village itself existed, at least in part, because of the volcanic ash in upland Kīpukakahaliʻi and the lowland kipuka.

Where the Chain of Craters Road parallels the coast, imagine how you could make a living there in this challenging landscape of lava flows. These flows are younger than the volcanic ash deposits at Kealakomo. Yet archaeological and historical studies show that people lived there in the 19th century. How could they do it?

It turns out that the lava flows are not quite as barren as they seem at first glance. Pockets of volcanic ash occupy depressions between many of the pāhoehoe toes. This ash fell during eruptions mainly in about 1650 and 1790 CE. Just after these eruptions, thin volcanic ash blanketed all the flows but was soon washed by rain into depressions, where it accumulated to form a meager, but suitable, soil for sweet potatoes and other crops. In this way seafood could be supplemented by locally grown produce, just enough to eke out an existence in this demanding environment.

Location, location, location. This realtor’s mantra applies equally to the effects of explosive eruptions at Kīlauea. At the summit, not so good. In the distance, not so bad.

Volcano Activity Updates

Kīlauea is not erupting. Its USGS Volcano Alert level is ADVISORY.

The unrest associated with the intrusion that began in early October southwest of Kīlauea’s summit continues. Low levels of earthquake activity have continued in the Southwest Rift Zone, summit, and upper East Rift Zone over the last week and a small swarm of earthquakes occurred the morning of December 1 south of the caldera. Unrest may continue to wax and wane with changes to the input of magma into the area and eruptive activity could occur in the near future with little or no warning. The most recent sulfur dioxide (SO2) emission rate for the summit—approximately 100 tonnes per day—was measured on November 17.

Mauna Loa is not erupting. Its USGS Volcano Alert Level is at NORMAL.

Webcams show no signs of activity on Mauna Loa. Summit seismicity increased slightly at the beginning of November but returned to low levels in the weeks since then. Ground deformation indicates continuing slow inflation as magma replenishes the reservoir system following the 2022 eruption. SO2 emission rates are at background levels.

Two earthquakes were reported felt in the Hawaiian Islands during the past week: a M3.2 earthquake 5 km (3 mi) S of Volcano at 1 km (1 mi) depth on Nov. 26 at 2:24 a.m. HST and a M3.9 earthquake 64 km (39 mi) SSW of Mākena at 0 km (0 mi) depth on Nov. 23 at 10:17 p.m. HST.

HVO continues to closely monitor Kīlauea and Mauna Loa.

Visit HVO’s website for past Volcano Watch articles, Kīlauea and Mauna Loa updates, volcano photos, maps, recent earthquake information, and more. Email questions to askHVO@usgs.gov.