A weekly feature provided by scientists at the Hawaiian Volcano Observatory.
July 5, 2012
Except for a little friction, Kīlauea's summit and rift zones are well connected
When William Ellis, the first Western visitor to the summit of Kīlauea, looked out over the broad and deep caldera in 1823, he noted that it "had been recently filled with liquid lava…and had, by some subterranean canal, emptied itself into the sea or upon the lower land on the shore." He was repeating an inference that had already been made by early Hawaiiansmagma drains from the summit to vents lower on the volcano's flank.
This simple and intuitive association has powerful implications for understanding Kīlauea. Most importantly, it means that there is a fluid connection from the rift zone to the summit during rift zone eruptions. When lava pours out of a rift zone vent, it drains magma from the summit magma chamber. Since Ellis' visit, many subsequent eruptions have reinforced this idea and, in modern times, sensitive geophysical instruments have actually measured the process.
Perhaps the best way of tracking the fluid connection between the summit and rift zone would be to simultaneously measure the lava level at each location through time. But until recently, there simply weren't any extended periods of simultaneous eruptions at the summit and rift zones (at least during the written historical period). The last four years, however, mark the first time in the past 500 years of long-term, simultaneous eruptions at the summit and rift zone. They provide the first opportunity for continuous observation of the lava level and, thus, the fluid connection, between the summit and the rift zones.
From 2011 to today, we have measured the level in the lava lake in Halemaʻumaʻu (at the summit) and Puʻu ʻŌʻō crater (on the east rift zone). During this time, three major eruptive events disrupted the system: the March 2011 Kamoamoa eruption, the August 2011 Puʻu ʻŌʻō draining, and the September 2011 fissure openings.
Overall, the lava levels in Halemaʻumaʻu and Puʻu ʻŌʻō closely followed one another, exhibiting the same peaks and troughs. Three sharp drops in lava level, manifested at both locations, resulted from the three eruptive events that depressurized the entire magmatic system. These simple measurements demonstrate a good "hydraulic" connection between the two vents.
Although these two vents show the same fluctuations, the lava level in Halemaʻumaʻu is, on average, about 80 m (260 ft) higher than the lava level in Puʻu ʻŌʻō at any given moment. If there is a good hydraulic connection, why don’t these lava levels equilibrate at the same elevation? In short, the answer may be friction. Water moving through pipes in your house, for instance, dissipates energy when it flows through bends, valves or fittings, because frictional forces effectively lessen the pressure in the fluid. If your home plumbing system has too many of these twists and turns, so much energy will be dissipated that you’ll have weak water pressure at the faucet. This effect, called hydraulic "head loss," is probably occurring in the conduit to the east rift zone, as well.
What are some implications of the hydraulic connection between the summit and east rift zone? First, the lava level provides another way (along with tilt, GPS, and seismicity) to track the pressure in the summit-to-east rift zone plumbing system, helping us anticipate new events. Periods when the lava level is very high in the system have preceded major changes in the east rift zone eruption, such as intrusions and new fissures, presumably due to the increased system pressure.
Second, a hydraulic connection means that changes can be transmitted in either direction in the system. When magma supply at the summit increases, it moves downrift and increases the eruption rate at the east rift zone. Conversely, in August 2011, we saw a drainage of Puʻu ʻŌʻō crater that was felt back at the summit (uprift), triggering partial drainage of the Halemaʻumaʻu lava lake.
There are broader implications for hazards, as well. Understanding the amount that summit lava levels drop during rift zone eruptive changes can help us understand the likelihood of powerful explosive eruptions at the summit. These explosions are thought to be triggered by lava draining to sufficiently low elevations that groundwater can infiltrate the hot magmatic system. This work is ongoing, but it shows that hydraulic principles can help shed light on volcanic "plumbing" systems.
Volcano Activity UpdateA lava lake within the Halemaʻumaʻu Overlook vent resulted in night-time glow that was visible from the Jaggar Museum overlook during the past week. The lake has been about 6080 m (200260 ft) below the floor of Halemaʻumaʻu Crater and visible by HVO's Webcam through much of the last month. This past week, the level fluctuated slightly due to several deflation-inflation (DI) cycles at the summit.
On Kīlauea's east rift zone, surface lava flows on the pali and coastal plain continued to be active. Over the past week, the flow front has advanced little and has lingered near the boundary of Hawaiʻi Volcanoes National Park about 950 m (0.6 miles) from the coastline; there was no active ocean entry. Within Puʻu ʻŌʻō, a lava pond was active in the eastern portion of the crater.
One earthquake was reported felt under the island of Hawaiʻi in the past week. On Tuesday, July 3, at 11:53 p.m., HST, a M2.9 earthquake occurred 4 km (3 mi) southwest of Pōhakuloa at a depth of 16 km (10 mi).
Visit our website (hvo.wr.usgs.gov) for past Volcano Watch articles, Kīlauea daily eruption updates, Mauna Loa weekly updates, volcano photos, recent earthquakes info, and more; call for summary updates at 808-967-8862 (Kīlauea) or 808-967-8866 (Mauna Loa); email questions to askHVO@usgs.gov.