During the past week, we have been keeping a close watch on the Northern Mariana Islands (NMI), as seismometers on the islands record high levels of seismicity from an undersea volcano near the island of Farallon de Pajaros. The seismic signals almost certainly herald an eruption. In fact, submarine explosions were heard by scuba divers conducting coral reef research in the area. The divers even felt the shock waves from the explosions, and one of the most powerful ones reverberated through the hull of the NOAA base ship, Hi‘ialakai, leading the crew to think something happened to the ship. Shipboard personnel also reported a large sulfur slick on the southeast coastline of Farallon de Pajaros.
Unfortunately, the ship had to leave the area under threat of an advancing typhoon. If they can get back to the vicinity soon, they might be able to investigate the source of the explosions with great caution, keeping in close contact with U.S. Geological Survey (USGS) and CNMI emergency management personnel, who are monitoring the seismicity.
The CNMI emergency management office and the volcano observatories of the USGS have been working together for more than 30 years to establish volcano monitoring networks and assess volcanic hazards in the Mariana Islands.
The most likely source of the current activity is Ahyi seamount, about 20 km southeast of Farallon de Pajaros. Ahyi rises to within 64 meters (210 feet) of the ocean surface and is associated with several reports of possible eruptions in historical times, the most recent in 2001.
Interspersed among the volcanoes that rise above sea level to form the NMI are many submarine volcanoes. Together, the islands and submarine volcanoes form the Mariana arc, a classic example of an island arc. These arcs, such as the Aleutians and the Japanese archipelago, are formed at subduction zones — boundaries where one tectonic plate plunges beneath another.
Reports of discolored water throughout the Mariana arc are common, indicating the NMI might experience frequent submarine eruptions. A dramatic, recent example is the 2010 eruption of South Sarigan seamount, which sent an eruption plume up to 12 kilometers (40,000 feet) above sea level.
The plume intersected many commercial air traffic routes, raising concern that the abrasive ash fragments could damage aircraft or even stall their engines. In addition, the eruption posed a potential hazard to ocean-going vessels, as it produced a large area of discolored water, possibly including a raft of pumice — a type of rock that can be produced in explosive volcanic eruptions. A recent submarine eruption of Havre seamount north of New Zealand in 2012 created a 20,000 square-kilometer (7,700 sqare-mile) raft of pumice — about twice the area of the Island of Hawaii — that eventually spread to about 4 million square-kilometers (1.5 million sqare-miles) as it broke up.
Pumice can float because it’s basically a type of foam — filled with gas bubbles encased in quickly cooled lava — which makes it less dense than the ocean water. It’s possible, but not certain, the current unrest near Ahyi seamount will escalate into a vigorous eruption, with the creation of pumice rafts, and even an explosive eruption column rising above sea level. If this happens, there are further possible threats of local disturbances of the water column that could result in local tsunami and ash fallout from the eruption plume.
Long-time readers of this column might be wondering about the possible outcomes of the seismic unrest we sometimes report on from our own submarine volcano, Lo‘ihi, off the south coast of Hawaii Island. The most recent confirmed eruption there, in 1996, created a large collapse pit at the summit. Deposits formed during that eruption and numerous previous eruptions, sampled by submersible vehicles, attest to frequent episodes of explosive volcanism at Lo‘ihi.
While there is no doubt Lo‘ihi is a very active volcano, the pressure of the approximately 1,000 meters (3,300 feet) of water between the top of the volcano and the surface makes it highly unlikely even the most vigorous of eruptions of Lo‘ihi will have significant impact at the ocean surface during our lifetimes.
Kilauea activity update
A lava lake within Halema‘uma‘u produced nighttime glow visible via HVO’s webcam during the past week.
The lake level was relatively high and stable, staying between 30 meters (98 feet) and 35 meters (115 feet) below the rim of the Overlook Crater.
On Kilauea’s East Rift Zone, the active front of the Kahauale‘a 2 flow was 8.3 kilometers (5.2 miles) northeast of its vent on Pu‘u ‘O‘o when mapped April 28.
In addition, two other flows, fed from spatter cones on the northern and southern edges of the crater floor, sent small flows toward the north and southeast, respectively. While the fate of the northern flow is not known, webcam images indicated, as of May 1, the southern flow was still active.
Poor views precluded views of the Kahauale‘a 2 flow, but it is expected to be active as well.
There were no earthquakes in the past week reported felt on the Island of Hawaii.
Visit the HVO website (http://hvo.wr.usgs.gov) for past Volcano Awareness Month articles and current Kilauea, Mauna Loa and Hualalai activity updates, recent volcano photos, recent earthquakes and more; call 967-8862 for a Kilauea summary; email questions to askHVO@usgs.gov.
Volcano Watch (http://hvo.wr.usgs.gov/volcanowatch/) is a weekly article and activity update written by scientists at the U.S. Geological Survey’s Hawaiian Volcano Observatory.