Volcano Watch — Pu‘u ‘Ō‘ō quietly and slowly building new flow field

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Without the dramatic flourish of recent events, lava is quietly erupting from Kīlauea's newest fissure, which opened September 21 on the east rim of Pu‘u ‘Ō‘ō crater. Lava is flowing out of sight directly into a growing lava-tube system and reappearing as small Pāhoehoe flows that extend nearly 3 km (2 miles) from the crater.

The flows are moving slowly southeast from Pu‘u ‘Ō‘ō, confined to a topographic low area between two major flow fields emplaced in the past 20 years.

The flow field to the north of the current flows was active 2007–2011 and erupted from the TEB vent, located about 2 km (1.2 miles) northeast of Pu‘u ‘Ō‘ō. A much larger flow field to the south was emplaced 1992–2007 from several vents active at different times along the southern flank of Pu‘u ‘Ō‘ō.

If the supply of lava to the new fissure and tube system continues uninterrupted, flows are expected to continue moving between the two flow fields. Remnants of the Royal Gardens subdivision are 3–4 km (2–2.5 miles) directly downslope.

Meanwhile, the eruption at the summit of Kīlauea in Halema‘uma‘u Crater continues with the lava lake relatively low, more than 100 m (328 ft.) below the rim.

With the eruption of the Pu‘u ‘Ō‘ō vent approaching its 30th year of activity and Halema‘uma‘u's eruption approaching its 5th, are there any signs that Pu‘u ‘Ō‘ō's activity may be waning?

One important measure of the potential demise of an erupting vent is the declining discharge, or effusion rate, of lava. During the last year of activity at the Kupaianaha vent, located 3 km (2 miles) downrift of Pu‘u ‘Ō‘ō, HVO scientists measured a declining rate of effusion. Lava discharge decreased in a linear fashion from about 250,000 cubic meters per day in April 1991 to about 54,000 cubic meters per day by November.

Kupaianaha stopped erupting in February 1992, and the activity completely moved back to Pu‘u ‘Ō‘ō.

Estimates of effusion rates were based on surveys using an instrument to measure very low frequency (VLF) electromagnetic signals across a single lava tube transporting lava from the vent. Lava is electrically very conductive and rock is not. The contrast permits the cross-sectional area of molten lava in a tube to be measured.

Combined with velocity measurements made through a nearby skylight, lava discharge can be estimated.

Unfortunately, the tube conditions needed to make these measurements have not existed since early 2007. Perhaps the new tube system will lead to the right conditions in the coming months for using this technique again.

A second but less direct measure of lava discharge before 2008 used the daily emission rate of sulfur dioxide gas. At Pu‘u ‘Ō‘ō, the amount of trapped gas that bubbled out of the magma reaching the surface was shown to correlate with the volume of the lava erupted as measured by the VLF method. For example, the release of about 2,000 tonnes of sulfur dioxide gas per day correlated to about 400,000 cubic meters of lava effusion.

For about 19 years prior to 2008, when the summit eruption began, sulfur dioxide emission rates correlated with VLF-based discharge estimates to within ten percent. When VLF measurements were not feasible, the gas emissions were used to estimate lava discharge.

The summit eruption, however, changed the gas-to-magma relationship at Pu‘u ‘Ō‘ō because of the significant amount of gas release occurring at Halema‘uma‘u Crater. Consequently, scientists haven’t been able to use gas emission rate method to estimate lava discharge for nearly four years.

With the changes in gas ratios and absence of tube conditions needed for VLF measurements, scientists have struggled to estimate Pu‘u ‘Ō‘ō's lava discharge.

The slow advance of the flow field—in comparison with the emplacement of the TEB flow field—appears to reflect a lower rate of lava effusion, but by how much, if any, cannot be known with confidence until a single tube develops with a nearby skylight.

Even with all the changes in the Pu‘u ‘Ō‘ō eruption in the past few years, including a possible but not quantifiable decrease in lava discharge from the newest vent on its cone, there does not appear to be a clear and present trend for anticipating the end of Pu‘u ‘Ō‘ō in the immediate future.


Volcano Activity Update

A lava lake was present within the Halema‘uma‘u Overlook vent over the past week, resulting in night-time glow that was visible from the Jaggar Museum overlook. The lake, which is about 100 m (328 ft) below the floor of Halema‘uma‘u and visible by Webcam, rose and fell slightly during the week in response to back-to-back deflation-inflation cycles.

Eruptive activity on Kīlauea's east rift zone was restricted to surface flows about 3.5 km (2.2 miles) east-southeast of Pu‘u ‘Ō‘ō. These flows travel through a lava tube that is fed by the September 21 fissure on the upper east flank of the Pu‘u ‘Ō‘ō cone. As of Thursday, November 3, the front of the active flows had reached the end of the ‘a‘ā flow that started this eruptive episode and which was active September 21–22, 2011.

No earthquakes beneath Hawai‘i Island were reported felt this past week.