February 28, 2002
A weekly feature provided by scientists at the Hawaiian Volcano Observatory.
Forecasting Lava Flow Speeds
Wouldn't it be nice to have eruption forecasts as rich in detail as our current weather forecasts, watches, and warnings? "This is your Hawai'i County Civil Defense. There is an eruption warning in effect until 0800 Wednesday morning with a 10% chance of lava flows advancing faster than 1 km/hr." We are a few discoveries away from such precision, but most would agree that this goal is probably attainable. For the second part of the forecast, however, we need considerably more information about lava flows than is currently available.
How fast can Hawaiian lava flows cover new ground? The fastest observed advance of a lava flow was during the 1950 Mauna Loa eruption, 9.3 km/hr (5.8 miles/hr). Most flows produced during the current eruption advanced quite a bit slower - up to 1 km/hr (0.6 miles/hr). They are not speedy - even the fastest Hawaiian lava flows of the last century would not have aroused the interest of those speed-cam operators lurking in parked vans.
In the 2000 years or so that people have been around to observe lava flows, few were well timed until the 1950 Mauna Loa eruption. This is a small data set - the only one that we have to estimate future potential lava flow speeds. The geologic record for Hualalai, Mauna Loa, and Kilauea are rich with hundreds of flows dating back many thousands of years, but the speeds of their emplacements were not recorded in any conventional fashion. Is there a way to time these older flows after the fact?
The good news is that there are some ways to determine lava flow velocities from these older flows. While advancing across the ground, lava flows can "run up" onto pre-existing features like cinder cones. The faster the flows advance, the larger the amount of run up. Examples of this can be found in the Kilauea 1823 flow, the Ka'upulehu flow from Hualalai, and the Mauna Loa 1950 flow. Lava flow advance velocities would be proportional to the square-root of the amount of vertical run up, according to college physics.
The bad news is that there are disagreements about how to interpret those features. The Kilauea and Hualalai examples have been interpreted by several scientists to indicate advance velocities of up to 54 km/hr (34 miles/hr). When that research became public, some newspaper accounts claimed that the lava must have flowed like water.
Their interpretations were so fantastic that the question deserved a second look. The same examples of run up were located and studied in detail, along with the entire flow. The "run up" turned out to be partly lava flow run up and partly spatter. The spatter was deposited much higher on these cones than the flow run up. In addition, each run up example was situated along a channel in the flow.
Our current thinking about these indicators is that the spatter was thrown up from lava in the nearby channel, not an advancing flow. We know that lava flowing in channels can travel more than 10 times faster than a lava flow advances. Thus, the combined spatter and run up on cones really tell us the lava velocity in the channel, not the lava flow advance rate.
Field research continues on these questions, ever hoping that it will improve our forecasting capabilities.
Eruptive activity of Kilauea Volcano continued unabated at the Pu`u `O`o vent during the past week. Glow from the area of the "rootless" shields can be seen above the brightness of the full moon. Flows on Pulama pali are crusted over, but lava has made its way to the base of the lava fan at the bottom of the pali. There are no surface flows in the coastal flats and no ocean entries.
One earthquake was reported felt during the week ending on February 28. A resident of Hilo felt an earthquake at 10:25 p.m. on February 23. The magnitude-2.6 earthquake was located 13 km (7.8 mi) northwest of the summit of Kilauea Volcano at a depth of 9.67 km (5.8 mi).
Updated: March 4, 2002 (pnf)