March 5 marked the second anniversary of the start of the Kamoamoa fissure eruption on Kilauea Volcano’s East Rift Zone. This small, but spectacular, eruption, which lasted only four days, March 5-9, 2011, was the culmination of a gradual pressurization of Kilauea that began months earlier.
In late 2010, as lava flows encroached on the Kalapana Gardens subdivision (destroying three homes), lava began to erupt within, and fill, the Pu‘u ‘O‘o crater. This suggested that more lava was reaching the East Rift Zone vent than could be carried away by the active lava tube system. The lava lake in Kilauea’s summit vent also began to rise, demonstrating the fluid connection between the volcano’s two eruption sites (Halema‘uma‘u and Pu‘u ‘O‘o). Moreover, the rate of seismicity along the upper East Rift Zone (near the summit) began to increase, along with the rate of extension and uplift in the summit area.
By March 5, 2011, lava had filled Pu‘u ‘O‘o’s crater to within 65 feet of its eastern rim, and the lava lake within the summit vent had risen to 215 feet below the floor of Halema‘uma‘u Crater.
Suddenly, at 1:42 p.m., tiltmeters near Pu‘u ‘O‘o recorded the start of rapid deflation, while nearby seismometers recorded a marked increase in tremor. The pressure within the underground pathway between Pu‘u ‘O‘o and the summit had become too great, causing the conduit to finally rupture. When it did, a dike — a bladelike body of magma — cut its way upward, splitting and shaking the ground as it rose. Minutes later, as magma was drawn away to feed the rising dike, the floor of Pu‘u ‘O‘o’s crater began to crumble and drop, and the summit lava lake began to drain.
Shortly after 5 p.m., the dike reached the ground surface, and lava began erupting about 1 mile west of Pu‘u ‘O‘o. This was the start of the Kamoamoa fissure eruption.
Over the next several hours, the new fissure migrated toward the east, eventually reaching a length of about 0.6 mile. It was joined early the next morning by a second fissure farther to the west, of similar length. The fissures were separated by about 0.25 mile of cracked and broken ground.
During the next two days, eruptive activity shifted from place to place within each fissure, and the overall vigor of the eruption increased. Lava fountains grew taller, and lava flows became more voluminous.
By March 8, the eruption had focused at two locations—one near the east end of the eastern fissure, and the other near the west end of the western fissure. The eastern fissure was dominated by the emission of gases, producing loud bursts, but little lava. The bits of lava thrown out accumulated around the vent to form a small, steep cinder and spatter cone. The western fissure, on the other hand, erupted a line of continuous fountains that formed a “wall” of lava. The comparatively high eruption rate of these fountains fed a fast-moving ‘a‘a flow that advanced through native forest to the southeast.
Activity at the eastern fissure waned overnight and stopped on the morning of March 9. The western fissure remained unchanged for a while longer, with its ‘a‘a flow reaching nearly 2 miles downslope. But its activity began to decline late in the afternoon, and by 10:30 p.m. on March 9, the Kamoamoa fissure eruption had come to an end.
The brief Kamoamoa fissure eruption was just an interlude in Kilauea’s long-lasting Pu‘u ‘O‘o eruption, active now for 30 years, but it provided new scientific insights about Kilauea’s plumbing system, and the geological and geophysical precursors offered a means of forecasting the eruption’s occurrence. Each event like the Kamoamoa fissure eruption helps us all prepare for events yet to come, some of which may not be so remotely located.
Kilauea activity update
A lava lake within the Halema‘uma‘u Overlook vent produced nighttime glow that was visible from the Jaggar Museum overlook and via HVO’s Webcam during the past week. The lake level fluctuated in response to summit deflation-inflation cycles, ranging between about 80-200 feet below the floor of Halema‘uma‘u.
On Kilauea’s east rift zone, breakouts from the Peace Day tube remain active above and at the base of the pali and on the coastal plain. Small ocean entries are active on both sides of the Hawaii Volcanoes National Park boundary. In addition, the Kahauale‘a flow, fed directly from a spatter cone on the northeastern edge of Pu‘u ‘O‘o’s crater floor, continues to advance slowly toward the northeast across a plain of 1980s-era ‘a‘a flows.
There were no felt earthquakes in the past week on the Island of Hawaii.
Visit the HVO website (http://hvo.wr.usgs.gov) for Volcano Awareness Month details and 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 is a weekly article and activity update written by scientists at the U.S. Geological Survey’s Hawaiian Volcano Observatory.