November 5, 2009
A weekly feature provided by scientists at the Hawaiian Volcano Observatory.
Evolving lava tube system spawns surface flows that reach the ocean
Dozens of small lava flows have moved down the pali and across the coastal plain of Kīlauea's south flank in the past several weeks as the nearly two-year-old tube system continues to evolve a network of underground conduits between the erupting vent and the ocean.
This is an interesting time for scientists and volcano watchers alike because of the dynamic nature of lava flow behavior. The flows have created new topography that redirects subsequent flows and formed tubes that can continue to spawn new surface flows as long as their cores remain molten or open. This behavior means that the coastal plain is likely to remain highly changeable in the days and weeks ahead.
The recent flows burned yet another structure (bringing the total to 209 since 1983), came to within 100 m (300 ft) of the trailhead leading to the lava viewing area maintained by Hawai`i County, and entered the ocean about 700 m (2,300 ft) west of the still-active ocean entry at Waikupanaha. The flows are also creating a new lava tube system adjacent to, and over, the main tube that has supplied lava to the ocean since March 2008.
Lava flowing in the tubes and on the surface erupts from the Thanksgiving Eve Breakout (TEB) vent, located about 1.6 km (1 mile) east of the Pu`u `O`o cone and 10.5 km (6.5 miles) from the ocean. Becoming active Thanksgiving eve on November 21, 2007, lava erupting from the TEB vent moved southward toward the ocean and, over the next several months, built a series of rootless shields, invaded the Royal Gardens subdivision, moved across the coastal plain, and reached the sea cliffs at the long-buried Waikupanaha pond on March 5, 2008.
As these flows moved progressively toward the ocean, a lava tube system developed behind the active flow fronts beneath their hardened crusts. When lava moves across the ground, a solid crust forms over the liquid almost instantly. The molten interior continues to move forward while the cooled, solidified crust is left above and behind to act as a conduit, or lava tube, that helps to feed more lava to the advancing flow fronts.
The well-established Waikupanaha tube system has often "leaked" lava to the surface - either from a skylight (collapsed roof) or along its side - to feed new surface flows in the past 18 months. In early October, the tube began leaking lava at the top of the pali to form flows along its east side. These flows formed the beginnings of a new tube system that is now supplying lava to flows on the coastal plain.
An important factor affecting the lava tube system and surface flows is the irregular eruption of lava at the TEB vent. For example, when the discharge of lava from the vent decreased on October 30, most of the surface flows stagnated, especially the ones next to the trailhead. When the discharge increased the next day, only a few small surface flows near the trailhead were supplied with new lava from the tube system; most of the lava was supplied to flows that crossed over the Waikupanaha tube and reached the ocean.
These changes in eruption rate from the TEB vent correlate with deflation-inflation cycles measured with tiltmeters at the summit and at the Pu`u `O`o cone. The cycles typically occur over a one- to two-day period. Deflation of the ground corresponds to reduced supply of magma to the TEB vent and inflation corresponds to increased supply.
At the time of this writing (November 5), the flows near the trailhead to the public viewing area are stagnant, but flows that crossed over the Waikupanaha tube in the past week are forming a new lava tube system above it and are still entering the ocean at the west end of the Waikupanaha delta. Also, the beginning of a new deflation-inflation cycle will likely affect the tube system and change the surface flow activity again this weekend.
Kīlauea Activity Update
Lava continues to erupt from the TEB vent on Kīlauea's east rift zone and flow through tubes to the ocean at Waikupanaha. A few sluggish surface flows were sporadically active near the end of the Kalapana access road adjacent to the Hawai`i County lava viewing area trail - at least through Thursday (the date of this writing). Other active surface flows were scattered over a broad area just inland from the coastline several hundred meters to the west of the end of the road. A new ocean entry started last weekend and has continued to built a small delta to the west of the Waikupanaha ocean entry.
Glow above the vent at Kīlauea's summit has been visible at night from Jaggar Museum. Small collapses of the floor of the Halema`uma`u Overlook vent cavity allowed sporadic webcam views of the spattering lava surface for part of the week. Volcanic gas emissions remain elevated, resulting in high concentrations of sulfur dioxide downwind.
No earthquakes beneath Hawai`i Island were reported felt this past week.
Visit our Web site (http://hvo.wr.usgs.gov) for detailed Kīlauea and Mauna Loa activity updates, recent volcano photos, recent earthquakes, and more; call (808) 967-8862 for a Kīlauea activity summary; email questions to askHVO@usgs.gov.
Updated: November 29, 2009 (pnf)