Volcano Watch — Kīlauea showing familiar pattern—or is it?

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Tuesday morning, July 31, started as a typical office day at the Hawaiian Volcano Observatory (HVO). Beginning at 10:25 a.m., a number of text messages and emails arrived in rapid succession. It was time to take a closer look.

Kīlauea showing familiar pattern—or is it?...

Hawaiian Volcano Observatory's Recent Earthquakes Web page from Tuesday, July 31, with earthquake shown as colored circles, according to their times of occurrence.

(Public domain.)

The messages all came from ENS, or Earthquake Notification Service. The U.S. Geological Survey (USGS) offers this service to subscribers who wish to automatically receive messages after earthquakes of specific interest to them. (https://sslearthquake.usgs.gov/ens/%5D. )

The earthquakes flagged in this series of messages all occurred beneath Kīlauea volcano's south flank. More specifically, they were concentrated beneath a section of Hilina Pali some 13 km (8 miles) south-southeast of the volcano's summit. We have focused on earthquakes in this region recently because of their apparent relationship to slow-slip events (SSE) that occur beneath Kīlauea's south flank. Was another SSE starting? What else might be going on?

It was easy to spot Tuesday's earthquakes on HVO's earthquake Web page. Other small clusters of earthquakes also appeared, extending from a few miles due west of Kīlauea's summit crater, into the summit caldera, and along Kīlauea's upper east rift zone. To be sure, these are familiar earthquake source regions to us, and we have a general understanding of what causes them and what their relationships to other processes are.

The earthquakes just west of Kīlauea's summit appear to have occurred along the downward extensions of faults comprising the easternmost part of the Ka‘ōiki fault system which lies between Kīlauea and Mauna Loa Volcanoes. These are "normal" faults where the "hanging" wall block moves downward relative to the "footwall."

Along the Ka‘ōiki faults, the southeastern, Kīlauea side of the faults has moved downward relative to the northwestern, Mauna Loa side. This is a natural part of the volcanoes' evolution, as their flanks slump seaward due to gravity.

Earthquakes clustering west of Kīlauea summit, in what we have called Nāmakanipaio or Ka‘ōiki Pali, sequences and swarms, are also consistent with slumping. Earthquake swarms here have preceded intrusions of magma from Kīlauea's summit into the east rift zone during the continuing Pu‘u ‘Ō‘ō eruption. Movements along these faults pulse neighboring parts of the volcano and have, at times, led to repeating patterns of earthquake and intrusive activity.

Earthquakes occurring beneath Kīlauea's summit caldera are related to magma accumulation and movement. Changes within the magma system stress the surrounding areas that produce earthquakes on nearby faults and cracks and within magma conduits in the caldera.

Along Kīlauea's upper east rift zone—delineated by the "Chain of Craters" in Hawai‘i Volcanoes National Park between the summit caldera and Mauna Ulu—earthquake swarms are directly associated with magma movement. Such swarms have coincided with other HVO observations and measurements to confirm their relationship to magma intrusions and eruptions. Tuesday's upper east rift zone earthquakes were not swarm-like, but rather, continued a trend of persistent, but low-level activity.

Since Tuesday, we have arrived at several conclusions. While eruptions continue in Halema‘uma‘u at Kīlauea's summit and at Pu‘u ‘Ō‘ō in its east rift zone, there was no large intrusion of magma from the summit into the rift zone. Such an intrusion, as might have been expected after seeing clustered earthquakes near Ka‘ōiki Pali, would have been heralded by more intense upper rift zone earthquakes. The Ka‘ōiki Pali earthquakes could be related to the earthquakes in Kīlauea caldera.

The recent Hilina Pali earthquakes do not appear to be signaling the start of another Kīlauea SSE. The most recent SSE occurred two months ago, and the next one would not be expected for roughly two years. There was a brief show of similar Hilina Pali events there in early July. Tuesday's earthquakes are plausibly very similar to those seen in July, but their connection to SSEs is not clear.

Kīlauea continues to erupt. Earthquakes continue in familiar locations but subsequent events do not always follow the same patterns. Meanwhile we're back to a typical day at HVO, keeping up with the incoming data and observations studying the different patterns and processes, and where they fit—or don't fit—together.

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Volcano Activity Update

A lava lake within the Halema‘uma‘u Overlook vent resulted in night-time glow that was visible from the Jaggar Museum overlook and by HVO's Webcam during the past week. The lake level fluctuated slowly between about 60 to 80 m (200–260 ft) below the floor of Halema‘uma‘u Crater, matching cycles of summit inflation and deflation. There were also several rise-fall cycles, during which the level fluctuated more rapidly.

On Kīlauea's east rift zone, surface lava flows on the coastal plain and pali have been relatively weak over the past week, with a few brief surges on the pali related to summit inflation and deflation. The active flow front was more than 1 km (0.6 miles) from the ocean. There was no active ocean entry. Incandescence was visible from three degassing vents within Pu‘u ‘Ō‘ō, including the pit on the northeastern side of the crater floor which has held a small lava pond. The lava pond was too low to be directly visible via Webcam.

One earthquake was reported felt under the island of Hawai‘i in the past week. A magnitude-3.4 earthquake occurred on Sunday, July 29, 2012, at 3:51 p.m., HST, and was located close to the Kahuā Ranch Office, 14 km (8 mi) south of Hala‘ula, at a depth of 20 km (12 mi).