by USGS Hawaiian Volcano Observatory

March 5, 2013, marked the 2nd anniversary of the start of the Kamoamoa fissure eruption on Kilauea Volcano’s East Rift Zone. This small, but spectacular, eruption, which lasted only 4 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 20 m (65 ft) of its eastern rim, and the lava lake within the summit vent had risen to 65 m (215 ft) below the floor of Halema`uma`u Crater.

Suddenly, at 1:42 p.m., HST, 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 5:00 p.m., the dike reached the ground surface, and lava began erupting about 2 km (1 mi) 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 1 km (0.6 mi). It was joined early the next morning by a second fissure farther to the west, of similar length. The fissures were separated by about 0.4 km (0.25 mi) 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 3 km (2 mi) 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.

TOP PHOTO: Lava spatters above the fissure just west of the base of Pu`u `O`o on March 6, 2011