In my last post we have looked at the different methods that are used to monitor the behaviour of a volcano. The observed behavioural patterns for the two active volcanoes on Hawai’i, Kïlauea and Mauna Loa, are fairly regular. The precisely recorded history of deflation and inflation is observing the times in which new magma is supplied or released into or from the volcano. The moving magma creates stress on the surrounding rocks causing different types of small earthquakes. During times of inflation, gradual volume changes in the magma chamber create high-frequency, short-period earthquakes. The magma release causing deflation is more abruptly and creates low-frequency, long-period earthquakes.
Top: Pattern showing the gradual inflation of Kïlauea and the rapid deflation after eruption. 1 microradian equals an ange of 0.00006 degree.
Bottom: Detailed 6 month observations of the Pu‘u ‘Ö‘ö-Kupaianaha eruption. In addition to the tilt record, it also shows the measured earthquakes. The two types of earthquakes mentioned in the text reflect times on inflation and deflation.
pubs.usgs.gov
The succession of inflation and deflation and seismic activity is seen in every eruption, but their size can vary drastically. Less common are patterns that go from deflation to inflation, called DI tilt events. These are typically short lived and have only been recognized since the early 2000’s. The eruption dynamics of these types of events are not well understood, but tend to correlate with lava pulses at Pu‘u ‘Ö‘ö, and maybe represent magma supply to a shallow magma chamber.
But with all this monitoring, how good can geologists predict Hawaiian eruptions?
The knowledge on how the Hawaiian volcanoes operate increases constantly, but geologists are still not able to accurately predict eruptions on a long-term base (one year or longer). The short-term forecast capabilities, on the other hand, are much better.
These short-term forecasts are based mainly on the above mentioned inflation-deflation patterns. When the level of inflation and the amount of short-period earthquakes is high the volcano is ready to erupt. This creates a time window of increased alertness, in which the exact moment of the eruption can vary. When eruption begins, a sharp deflation and earthquakes close to the site of eruptive outbreak can be measured. These measurements usually precede the surface outbreak of the lava by a few hours, leaving a small time window for geologists to issue warnings.
Generally speaking, the geologists from the Hawaiian Volcano Observatory can accurately identify the increased potential for eruptions at Kïlauea and Mauna Loa and locate likely locations of lava outbreaks, but cannot make exact forecasts on eruption timing and size.
In recent years, to increase forecasting abilities, additions to the seismic and ground-deformation monitoring techniques have been developed. One of these techniques is the measurement and monitoring of composition and volume of volcanic gas emissions. Measurement capabilities of down to 1 part in a million (ppm) enables geologists to detect the slightest changes that can be used to identify the evolution of the magma below. They also help to estimate the potential hazard from volcanic air pollution.
Other techniques include magnetic, gravity, and geoelectrical studies. These enable a better understanding of magma movement below the surface, but have not been used to identify definitive short-term precursors to eruptions.
Previous Posts
Hawaiian volcanoes - Part 1: Introduction
Hawaiian volcanoes - Part 2: The Hawaiian Hotspot
Hawaiian volcanoes - Part 3: A growing volcano
Hawaiian volcanoes - Part 4: The Rejuvenation Stage
Hawaiian volcanoes - Part 5: Evolution to Atolls and Seamounts
Hawaiian volcanoes - Part 6: Mythology vs Geology
Hawaiian volcanoes – Part 7: Recent eruptions
Hawaiian volcanoes – Part 8: Volcano Monitoring
