On the afternoon of April 30. 2018, an earthquake “swarm” in Hawaii Island began such that earthquakes started to occur far more frequently, up to 10 per hour. As this animation shows, a swarm of volcanic earthquakes began northwest of the summit of Kilauea Volcano on its East Rift Zone, a feature extending from Kilauea’s summit that carries magma underground through the flank of the volcano. The occurrence of these earthquakes then moved along the rift zone away from the summit, suggesting the movement of magma below ground in this direction. Magma reached the surface and erupted as lava on the afternoon of May 3 and is ongoing (6 May 2018). Since the eruption began the frequency of volcanic earthquakes has dropped to about 1 per hour. However, tectonic earthquakes that result from motion on faults became more common since the eruption, many larger than magnitude 4.0 with the largest having a magnitude of 6.9 on the afternoon of May 4.

Time-lapse thermal image movie of Halemaumau Overlook Vent. April 26, 2018 to May 6, 2018. Images courtesy of USGS/HVO

The summit lava lake has dropped significantly over the past few days, and this evening was roughly 220 m below the crater rim. This very wide angle camera view captures the entire north portion of the Overlook crater. Photo taken Sunday, May 6, 2018 courtesy of U.S. Geological Survey

An intrusion of magma into Kīlauea Volcano’s lower East Rift Zone resulted in an eruption in Leilani Estates in the lower Puna District on the Island of Hawaiʻi. The first four fissures to erupt in the subdivision are shown here on May 4, emitting copious amounts of hazardous sulfur dioxide gas. Pu‘u ‘Ō‘ō (top center), which is about 20 km (12.4 mi) uprift of Leilani Estates, can be seen on the far horizon (top center). As of May 6, at least 10 fissures have erupted in the subdivision. USGS photo by T. Neal.

With each large earthquake, ground shaking causes additional collapse within the Pu‘u ‘Ō‘ō crater, sending a plume of reddish-brown ash skyward. The size and vigor of a plume depends on the size of the earthquake and subsequent collapse. This roiling ash plume followed the magnitude-6.9 earthquake on May 4. Much of the rock within the crater is rust in color, which is a result of heavy alteration by acidic volcanic gases. When the rock is pulverized by a collapse event, the resulting ash plume is pink to reddish-brown ash plume. USGS photo by T. Neal.

Over 500 earthquakes were located by the USGS Hawaiian Volcano Observatory (HVO) between noon Friday and noon Saturday, May 4-5, 2018. A magnitude-6.9 earthquake at 12:32 p.m. HST on Friday was preceded by two foreshocks with magnitudes of 5.4 and 4.4 at 11:32 a.m. and 11:38 a.m., respectively, and followed by eight aftershocks with magnitudes greater than 4.0, including a magnitude-5.3 at 2:37 p.m. Moderate to strong aftershocks should be expected for weeks to months to come. The earthquakes are related to the ongoing intrusion into Kīlauea’s East Rift Zone and reflect adjustments beneath the south flank of the volcano. USGS map.

Kīlauea’s summit eruption within Halemaʻumaʻu did not initially respond to the volcano’s East Rift Zone activity (collapse of the Pu‘u ‘Ō‘ō crater floor and magmatic intrusion into the rift zone) on April 30. But on May 2, the lava lake level began to drop in concert with summit deflation, suggesting that magma was moving from the summit into the East Rift Zone. By Friday, May 4, when this photo was taken, the lava lake level had dropped 85 m (279 ft). The lake continues to drop. Lava that spilled from the lake and onto the floor of Halemaʻumaʻu during April 21-27 formed the dark-colored flows that can be seen on either side of the lava lake. USGS photo by J.Babb.

(Volcano Watch is a weekly article written by scientists at the U.S. Geological Survey’s Hawaiian Volcano Observatory.)

The USGS Hawaiian Volcano Observatory was unable to issue “Volcano Watch” by its regular Thursday deadline on May 3 due to unfolding events on Kīlauea Volcano. Little did we know that Friday would be even more hectic.

How it began: Following a collapse of the Pu‘u ‘Ō‘ō crater floor on Monday, April 30, an intrusion of magma migrated down Kīlauea’s East Rift Zone, advancing below ground toward Highway 130 and communities in the lower Puna District on the Island of Hawaiʻi. The possibility that the intrusion would lead to an eruption of lava became more likely as numerous small earthquakes shook the area over the next few days.

On Thursday, May 3, it happened! With little fanfare, steaming ground cracks were soon spewing lava in Leilani Estates.

By Friday morning, three additional fissures had opened in the subdivision, with lava traveling less than a few tens of meters (yards) from the vents.

Then, Kīlauea really started rocking and rolling. It began with a magnitude-5.4 earthquake at 11:32 a.m. HST. An hour later, a magnitude-6.9 earthquake, the strongest quake to strike Hawaiʻi since 1975, rattled residents across the island and beyond, with felt reports from as far away as Kaua‘i. Over the next 24 hours, more than 500 earthquakes—13 with magnitudes of 4 or greater—shook the island.

In the meantime, the summit of KÄ«lauea switched from inflation to deflation, and in concert with that deflation, the summit lava lake level began to drop.

Events of this notable day on KÄ«lauea are summarized in a photo essay featuring images from Friday, May 4, 2018.

An eruption has commenced in the Leilani Estates subdivision in the lower East Rift Zone of Kīlauea Volcano. White, hot vapor and blue fume emanated from an area of cracking in the eastern part of the subdivision. Spatter began erupting shortly before 5:00 p.m. HST. Lava was confirmed at the surface in the eastern end of the subdivision, in the areas of Mohala and Leilani Streets. According to the Hawai‘i County Civil Defense update at 5:40 p.m., all residents in Leilani Estates and Lanipuna Gardens Subdivsions are required to evacuate. Photo taken Thursday, May 3, 2018 courtesy of U.S. Geological Survey

At 10:30 HST, ground shaking from a preliminary magnitude-5.0 earthquake south of Pu‘u ‘Ō‘ō caused rockfalls and possibly additional collapse into the Pu‘u ‘Ō‘ō crater on KÄ«lauea Volcano’s East Rift Zone. A short-lived plume of ash produced by this event lofted skyward and dissipated as it drifted southwest from Pu‘u ‘Ō‘ō. Downwind areas may have experienced a dusting of ash from this plume. At this time, the 10:30 earthquake has caused no other changes at KÄ«lauea Volcano. HVO will continue to closely watch monitoring data for any changes. This image was captured from an HVO overflight carrying HVO scientists to the East Rift Zone for field work today. USGS photo by Kevan Kamibayashi.

The opening phases of fissure eruptions are dynamic. Additional vents and new lava outbreaks may occur. The fissure in Leilani Estates (as of 6:00 p.m.) was about 150 m (164 yards) long. Photo taken Thursday, May 3, 2018 courtesy of U.S. Geological Survey

Areas downslope of the erupting vent are at risk of lava inundation. At this time, the general area of the Leilani Estates subdivision appears at greatest risk. Hawai‘i County Civil Defense is on scene and coordinating needed responses, including evacuation of the Leilani Estates and Lanipuna Gardens subdivisions. Photo taken Thursday, May 3, 2018 courtesy of U.S. Geological Survey

Residents of the lower Puna District should remain alert, review individual, family, and business emergency plans, and watch for further information about the status of the volcano. Hawai‘i County Civil Defense messages may be found at http://www.hawaiicounty.gov/active-alerts/. Photo taken Thursday, May 3, 2018 courtesy of U.S. Geological Survey

After a long period of rain and low clouds, improved weather and high clouds today allowed good airborne observations of the collapse crater in Pu‘u ‘Ō‘ō. This photo looks to the east, and shows the deep collapse crater formed on Monday, April 30, when magma beneath Pu‘u ‘Ō‘ō drained. For scale, the crater is about 250 meters (820 feet) wide. Photo taken Thursday, May 3, 2018 courtesy of U.S. Geological Survey

This wide shot looks northeast, and shows the fissure that formed on the west flank of the Pu‘u ‘Ō‘ō cone (line of white steam). The fissure extends roughly 1.5 km (0.9 mi) west of Pu‘u ‘Ō‘ō Crater, and nearly reaches the bottom of the photograph. Photo taken Thursday, May 3, 2018 courtesy of U.S. Geological Survey

Another wide view, from the east, showing the dust-rich plume and coating of reddish ash to the south of Pu‘u ‘Ō‘ō. Photo taken Thursday, May 3, 2018 courtesy of U.S. Geological Survey

A view of Pu‘u ‘Ō‘ō from the east, shortly after a small collapse. The coating of red ash on the south side of the cone (left side of photo) is evident. Photo taken Thursday, May 3, 2018 courtesy of U.S. Geological Survey

At 10:31 a.m. HST, while HVO geologists were working on Pu‘u ‘Ō‘ō, a magnitude-5.0 earthquake shook the ground around the cone. Moments later, a collapse occurred in the crater of Pu‘u ‘Ō‘ō, creating a robust, reddish-brown ash plume. Photo taken Thursday, May 3, 2018 courtesy of U.S. Geological Survey

HVO geologists confirmed that the Episode 61g flow is now inactive. Thermal images showed no active breakouts on the flow field. This photo shows the area where breakouts were focused prior to magma draining from Pu‘u ‘Ō‘ō earlier in the week. Photo taken Thursday, May 3, 2018 courtesy of U.S. Geological Survey