April 30, 1995

A weekly feature provided by scientists at the Hawaiian Volcano Observatory.

Kilauea Lava Flow Status

The 12-year-long eruption on Kilauea's east rift zone continues, with vents on the southwestern flank of the Pu`u `O`o cone feeding directly into lava tubes. These tubes form within active lava flows and initially are very shallow. Over time, however, the tubes erode their base and gradually downcut to deeper and deeper levels. Near the vents, tubes are over 100 feet below the surface of the flows. Below the 2,300-ft elevation, the tube is shallower, and occasionally its roof collapses, resulting in "skylights." Despite these collapses, the tube is relatively stable down to the top of Pulama Pali, at about the 2,100-ft elevation. There have been no surface lava flows, i.e., breakouts from weak points in the tube, above this elevation for over a year. Below this point, however, the tube system is less stable because of the steep slope of Pulama Pali, and breakouts are common.

For the past six months, we have witnessed a period of prolonged surface flow activity below the 2,100-ft elevation, with channeled `a`a flows on the slope of Pulama Pali and broad sheets of tube-fed pahoehoe breaking out on the coastal plain. The lava owes this period of high visibility to a series of three eruptive pauses in October and November and two more in March and April. Following each pause, the tube is reoccupied from the vents to the top of Pulama Pali, then breaks out to form new surface flows which follow a path of least resistance toward the coast. Since last October, there have been 15 separate ocean entries, lasting from one to four weeks, along nearly two miles of coast between Kamokuna and Highcastle.

Over the past three weeks, most of the nearly 400,000 cubic yards per day of lava issuing from the vent has flowed toward the western side of the flow field. Prior to the latest pause on April 11, lava was entering the ocean at Highcastle and Lae`apuki. Since the pause, we are once again seeing many surface flows on Pulama Pali and the coastal plain. Fed by the western flow, a large lava delta continues to grow beneath the sea cliff at Highcastle. This flow is continuing to expand along its west and east margins. Lava is also entering the ocean at Kamoamoa but at relatively low volume. Lava viewing from the end of Chain of Craters Road has been fantastic!

Recent pauses in the eruption of Kilauea's east rift zone are typically associated with an increase in seismicity and deformation of Kilauea's summit, thus demonstrating a direct connection between the Pu'u 'O'o vent area and the magma chamber which resides beneath the summit caldera. The first sign of a pause frequently comes many hours after it actually begins as the lava output at the ocean declines. Thus, it is difficult to determine whether the summit activity is a precursor or a response to the start of a pause. In order to better determine the timing of the pauses, we have deployed a thermocouple that continuously records the air temperature in the main lava tube approximately one mile from the vents. Recent data suggest that the "tube-tattler," which is suspended in the tube through a skylight at the 2,250-ft elevation, is able to detect changes in the volume of lava flowing through the tube and, thus, records the drop in volume when a pause begins. According to the tube-tattler, the latest pause in the eruption occurred just after midnight on April 10 and lasted for 17 hours. Inflation and subsequent deflation at the summit of Kilauea, accompanied by swarms of small earthquakes, occurred during a 14-hour period prior to the time when lava ceased flowing from the vent. The tale told by the tube-tattler, in conjunction with deformation and seismic data, helps us predict eruptive behavior and interpret the magmatic plumbing system that supplies the current eruption.

The Volcano Watch is a weekly feature prepared by U.S.G.S. scientists at the Hawaiian Volcano Observatory.