Kilauea’s 2018 summit collapse dramatically transformed the geometry and appearance of Halema‘uma‘u crater and Kilauea caldera.
Last week’s “Volcano Watch” article described how the 2018 events impacted the magma plumbing system beneath the surface of Kilauea’s summit. This week, we’ll explore how the 2018 events impacted the geologic deposits on the surface.
Kilauea’s summit is no stranger to change.
Several summit drainages or collapses in the 19th and early 20th centuries are documented in early western accounts. The Rev. William Ellis, author of the first written description of Kilauea, observed of the summit in 1823 “… that the crater had been recently filled with liquid lava … and had, by some subterranean canal, emptied itself into the sea, or inundated the low land on the shore.”
Ellis’ description hypothesizes that Kilauea’s summit had been erupting before a flank eruption drained the summit. Indeed, an eruption of Kilauea’s Southwest Rift Zone in 1823 might have contributed to the summit collapse that Ellis described, much like Kilauea’s summit collapse in 2018 was accompanied by the lower East Rift Zone eruption.
Kilauea’s summit was partially drained, sometimes leading to enlargement of Halema‘uma‘u or collapse of portions of the caldera floor, in 1823, 1832, 1840, 1868, 1886, 1891, 1894, 1916, 1919, 1922, 1924 and 2018. It’s unclear why Kilauea summit collapses were less frequent in the past century, but perhaps prolonged flank eruptions on the middle East Rift Zone (Mauna Ulu 1969-74 and Pu‘u ‘O‘o 1983-2018) played a part.
Some Kilauea summit drainages or collapses were accompanied by lower-elevation flank eruptions; others, by likely “failed” eruptions, wherein magma intruded into the flank of the volcano but wasn’t erupted onto the surface.
In the past, Halema‘uma‘u crater was described as being transformed into a pit of “tumbled masses of rock blocks” after a drainage or collapse of Kilauea summit. This description is certainly applicable to the current appearance of Halema‘uma‘u, with its steep crater walls and rubble base.
Nineteenth-century descriptions of Kilauea summit after a collapse sometimes describe a “black ledge” — evidence of summit lava-lake activity — bordering collapsed areas. Though there was a summit lava lake before the 2018 collapse, it left no such “black ledge”; those deposits are now part of the rubble at the base of Halema‘uma‘u. The 2018 collapse almost completely erased the geologic evidence of Kilauea’s 2008-18 summit lava lake!
How did the 2018 summit collapse impact other geologic deposits within Kilauea caldera?
A comparison of pre- and post-2018 geologic maps shows that before 2018, the floor of Halema‘uma‘u crater consisted of lava flows erupted in 1974 and 1982 and overflows from the 2008-18 summit lava lake. All of these deposits are now part of the rubble at the base of the current (post-2018) Halema‘uma‘u. Now, another type of lake (water) occupies the bottom of the crater, although not in the same location as the 2008-18 lava lake.
The 2018 Kilauea summit collapse also impacted a broader area of Kilauea caldera. Before 2018, Kilauea caldera floor was a mosaic of different-aged lava flows — 19th century flows that inundated much of the caldera floor mostly overlain by more recent flows from summit eruptions in 1918-19, 1919, 1921, 1954, 1971, 1974, 1975 and 1982.
During the many earthquakes that accompanied the collapse events of 2018, these deposits on the floor of Kilauea caldera were jostled, cracked and shifted. Portions of them were lowered more than 100 meters (yards) and likely shifted laterally several tens of meters (yards).
Fragments of these older lava flow deposits remain intact on the “down-dropped blocks” that formed within Kilauea caldera during 2018. Lava flows from 1919 and 1974 are on the surface of the smaller down-dropped blocks, and numerous lava flows erupted during the past 150 years remain on the largest of the down-dropped blocks.
More detailed future geologic mapping will reveal how much these deposits were impacted by Kilauea’s 2018 collapse. A previous “Volcano Watch” article describes the new outcrops exposed in the fault scarps formed during 2018 and their importance to better understanding Kilauea’s eruptive history.
Changes to Kilauea’s summit as a result of the 2018 collapse are profound, but not permanent.
As the record during the past two centuries demonstrates, Kilauea’s summit will erupt and collapse again (and again), repeatedly transforming the summit geometry and appearance in the process.
Volcano activity updates
Kilauea Volcano is not erupting. Its USGS Volcano Alert level remains at Normal (https://volcanoes.usgs.gov/vhp/about_alerts.html). Kilauea updates are issued monthly.
Kilauea monitoring data for the past month show variable but typical rates of seismicity and ground deformation, low rates of sulfur dioxide emissions and only minor geologic changes since the end of eruptive activity in September 2018. The water lake at the bottom of Halema‘uma‘u continues to slowly expand and deepen. For the most current information about the lake, visit https://volcanoes.usgs.gov/volcanoes/kilauea/summit_water_resources.html.
Mauna Loa is not erupting and remains at Volcano Alert Level Advisory. This alert level does not mean an eruption is imminent or progression to eruption from current level of unrest is certain. Mauna Loa updates are issued weekly.
This past week, about 70 small-magnitude earthquakes were recorded beneath the upper elevations of Mauna Loa; most of these occurred at shallow depths of less than 8 kilometers (about 5 miles). GPS measurements show long-term slowly increasing summit inflation, consistent with magma supply to the volcano’s shallow storage system. Gas concentrations and fumarole temperatures as measured at Sulphur Cone and the summit remain stable. Webcams show no changes to the landscape. For more information about current monitoring of Mauna Loa Volcano, visit https://volcanoes.usgs.gov/volcanoes/mauna_loa/monitoring_summary.html.
There were five events with three or more felt reports in the Hawaiian Islands during the past week: a M2.9 earthquake 14 km (8 mi) N of Kukuihaele at 23 km (14 mi) depth at 5:47 p.m. Sept. 9, a M3.0 earthquake 8 km (4 mi) E of Pahala at 32 km (20 mi) depth at 12:18 a.m. Sept. 9, a M3.4 earthquake 1 km (0 mi) SE of Pahala at 31 km (19 mi) depth at 2:19 a.m. Sept. 6, a M2.6 earthquake 15 km (9 mi) N of Pahala at 9 km (6 mi) depth at 5:04 p.m. Sept. 5 and a M3.7 earthquake 2 km (1 mi) N of Hali‘imaile at 31 km (19 mi) depth at 9:43 p.m. Sept. 4.
HVO continues to closely monitor Kilauea and Mauna Loa for any signs of increased activity.
Visit HVO’s website for past “Volcano Watch” articles, Kilauea and Mauna Loa updates, volcano photos, maps, recent earthquake information and more. Email questions to askHVO@usgs.gov.
“Volcano Watch” is a weekly article and activity update written by U.S. Geological Survey Hawaiian Volcano Observatory scientists and affiliates.