Gas studies at HVO are conducted in order to assess the current eruptive activity and hazards of Kilauea and Mauna Loa Volcanoes and to develop and test new volcanic gas monitoring techniques for use in Hawai`i and elsewhere. These two goals help us to develop better models of how volcanoes work. Gas studies also support research on global climate change by improving our estimates of gas emission budgets for hot-spot volcanoes. On a more local level, the current long-lived eruption of Kilauea has increased island and state-wide concern and awareness of the effects of volcanic smog (vog) on environmental health. Current gas studies conducted at HVO help characterize and quantify ambient concentrations of volcanic pollutant gases.

At Kilauea, sulfur dioxide (SO₂) emission-rate measurements have been collected nearly weekly since 1979 using a correlation spectrometer (COSPEC). These measurements constitute an unusually complete data set. They show that Kilauea releases between 300,000 and 700,000 metric tons of SO₂ yearly during long-lived eruptions, such as the current one, and less than 75,000 tons when the volcano is quiescent. These ground- based, remote, SO₂ measurements have been used to calibrate space-based and high-altitude airborne measurements. Since SO₂ is a greenhouse gas, these emission-rate measurements are also important for assessing volcanoes as agents of climate change. In addition, emission rates for other gases and metals that are difficult to measure directly can be estimated by combining SO₂ emission rate and concentration data.

Chemical analysis of gas samples taken from volcanic vents at the summit and rift zones of Kilauea and Mauna Loa has helped to improve our models of how these volcanoes release volatiles. Carbon/sulfur concentration ratios indicate that summit gases are richer in carbon dioxide (CO₂) than are rift gases, because CO₂ is less soluble in basaltic magma than the other gases, so that it is given off during shallow storage beneath the summit. Carbon/sulfur ratios are measured about weekly at the summit of Kilauea.

Continuous monitoring of gases released from Kilauea using multi-species chemical sensors shows that events of heightened gas emission can occur on a time scale too short to be detected, either by intermittent gas sampling with laboratory analysis or by emission rate measurements. A network of continuously monitoring stations using chemical sensors for individual gas species is under development. This network will complement other geochemical and geophysical time-series measurements.

Another type of continuous monitoring is done in cooperation with the National Park Service. Monitoring of ambient air quality provides information about the impact of volcanic emissions on air quality. These studies have documented the importance of wind speed and wind direction on the geographic fate and concentration of volcanic air pollution on the Island of Hawaii. The data show that federal health standards for SO₂ have been exceeded more than 70 times during the last ten years within Hawai`i Volcanoes National Park.

Geologists at HVO study eruptions and their products in order to better understand Hawaiian volcanoes and reduce their risk. This study takes a wide variety of directions, from evaluating the deposits of past eruptions to making dynamic measurements of ongoing eruptions. Results of these studies are used to develop ideas about how Hawaiian volcanoes erupt, how magma moves underground, how lava spreads across the landscape, how explosive eruptions take place and what causes them, how physical and chemical changes take place within the magma and lava, and a host of other topics all focused on eruption activity and its impact on society in Hawai`i.

For example, geologists at HVO track the advance of active lava flows using GPS mapping aids and aerial photographs. This information enables County, State, and Federal personnel to respond to imminent hazards that may affect individuals and communities. Observatory scientists keep detailed descriptions and photo archives, including still and video images, to better understand and forecast future eruptions. Lava, spatter, and other erupted material are sampled for study of their geochemical and mineralogic composition. Geodetic surveys let us precisely depict the growth of flow fields and vents. In coastal areas, we study the growth and destruction of new land at the ocean's edge and the hazards associated with these processes. These investigations provide the long-term basis for understanding how magma is transported to the shallow crust, stored, and erupted from the summit and rift zones of active volcanoes.

Our studies go beyond the study and documentation of lava flows erupted by Kilauea and Mauna Loa. Observatory investigations also target other active volcanoes in Hawai`i, including Hualalai and East Maui (Haleakala) volcanoes. These volcanoes have erupted in the past 200 years or so and are capable of erupting in the future. We determine their eruptive histories by radiocarbon dating and detailed studies of the stratigraphic sequence of lava flows and explosive deposits. Recurrence intervals of eruptions, changes in vent locations, and probabilistic evaluations of future activity are results of intensive field study, including geologic mapping and sampling.

Explosive eruptions have occurred rather often in the past from Kilauea and other Hawaiian volcanoes. The products of these explosions are studied in order to learn more about what causes the explosions. Also, active faults occur on Kilauea and Mauna Loa, and detailed analysis of past faulting events, as determined from field study, is used to anticipate future events. Detailed geodetic networks monitor the fault zones, and frequent measurement detects ongoing movement within the zones.

The ground around active volcanoes is always moving. These movements are usually subtle and can be measured only with very sensitive instruments using specialized techniques. Measurements of surface deformation are used to assess what is happening inside a volcano. For example, a radial pattern of outward movement or tilt indicates that pressure in a buried magma chamber is increasing. This could result from a steady influx of magma, the arrival of a new surge of magma, or a sudden increase in entrapped magmatic gas. Earthquakes and adjustments of the unstable volcanic edifice can also produce ground tilts and displacements. The largest ground movements accompany large earthquakes and the formation of dikes and other intrusive magma bodies. The active volcanoes of Hawai`i provide a natural laboratory to develop and test new volcano-monitoring techniques.

At HVO, we collect accurate and timely ground-deformation data to monitor Hawaiian volcanoes. We use a variety of techniques and instruments and apply them over a broad range of space and time scales. Data from tiltmeters are sampled every 10 minutes and provide our only real-time deformation monitor. Continuous Global Positioning Survey (GPS) data are sampled every 30 seconds, but we currently download the data only once a day and calculate one-day average positions. We conduct periodic (one or more times per year) leveling, GPS, and EDM (electronic distance measurement) surveys. Each survey or data point can be compared with previously sampled data to determine accumulated ground deformation and to calculate strain rates or velocities. HVO is currently upgrading its deformation-monitoring program to emphasize real- time monitoring of Mauna Loa and Kilauea. This upgrade includes new installations of borehole dilatometers and tiltmeters, new installations of continuously recording GPS receivers, improved data logging and telemetry, and development of strain analysis and pattern recognition software. Our goal is to be able to track magma intrusions and strain events as they happen. Work on this upgrade began in September 1997 and is expected to be mostly completed by September 1999.

Our existing real-time deformation-monitoring network consists of three shallow (1 m deep) borehole tiltmeters, two deep (7 m) borehole tiltmeters, and one single-component platform tiltmeter placed in a buried vault. Automatically updated displays of these data are available at HVO. These data allow us to track short-term (minutes to days) events primarily associated with pressure and other changes in the volcano's magma system.

Near real-time deformation monitoring is done with a network of sixteen continuous GPS stations. This network is a cooperative effort between HVO, Stanford University, and the University of Hawai`i. Automatically updated displays of these data are available at HVO. We are working on downloading and producing solutions as frequently as every 30 minutes. These data allow us to track mid- to long-term changes (days to years) associated with the magma system and tectonic movements.

Quarterly to annual campaign-style surveys are used to track long-term deformation of the volcanic edifice. Each survey provides a snapshot of the elevations and positions of the bench marks that can be compared with those of previous surveys to determine accumulated ground deformation. GPS and leveling surveys are currently our primary long-term monitoring tool.

Summary of HVO's Deformation-monitoring Networks and Instruments

The HVO tiltmeter network shrunk from over 14 stations in the early 1980's to the current five stations by the 1990s. The old installations were in shallow (1-m deep) boreholes and were subject to noise from diurnal and seasonal temperature changes. We installed two prototype tiltmeters in late 1997 using improved instruments and deeper (7-m deep) installations. The prototype installations provide increased sensitivity to tilt and require improved data loggers to exploit. We are upgrading from a 12-bit radio-based polling system to a 18-bit dual radio GOES satellite based polling system. We will be installing a GOES downlink station to record the data. The data will also be recorded with a parallel system in Menlo Park, California. In 1998, two new tiltmeters will be installed on Kilauea's east rift zone and another four will be installed on Mauna Loa's summit and rift zones.

In addition to the 16 sites monitored with continuously recording GPS receivers, about 120 sites are surveyed using static GPS survey techniques every year. We expect the number of these infrequently occupied GPS sites to grow as we implement short-occupation and kinematic-survey techniques. NASA Gipsy-Oasis software is used to obtain position solutions for all static surveys. We use Rapid Service and final orbits provided by NASA's Jet Propulsion Laboratory in our data reduction. Solutions provide positions accurate to a few millimeters in the horizontal components and about a centimeter in the vertical component.

We monitor elevation changes on level-line networks that have a total length of nearly 400 km. Tilt is also deduced from elevation changes within 110 equilateral triangle (approx. 40 m base) tilt arrays. The various leveling networks are measured at irregular intervals; rapidly deforming areas are surveyed more frequently. A subset of the tilt arrays and level lines on the summit and rift zones of Kilauea and Mauna Loa is measured annually. Because of the rapid changes and the magnitude of the signals recorded, surveys conducted to second-order first-class standards provide both fast and accurate results. On most of the networks, instrument setups are marked, and turning points are nailed and marked to help expedite the surveys. Tilt arrays are measured to first-order standards, excluding temperature corrections. Two pairs of Wild 3-m long invar rods and two Wild NA-2 level instruments with parallel micrometer plates are used for the leveling surveys. Three Wild 3-m long invar rods with stays and the Wild NA-2 level instrument with parallel micrometer plate are used for the tilt surveys. Field data are recorded on a MC-II hand-held calculator and are downloaded and stored on a VAX server at HVO. We are incrementally upgrading to a digital level, having purchased bar-coded rods in 1998. These rods are used with a borrowed digital level.

With the exception of a few lines, all EDM survey network data in the 1970s and 1980s were reduced with end-point meteorological measurements. The HVO trilateration-horizontal strain network consists of more than 750 lines on Kilauea, Mauna Loa, and Hualalai. Only a few of those lines have been measured since 1993, when we converted to GPS. Most current EDM surveys are limited to measurements of permanently mounted reflectors (31 lines on Kilauea and 25 lines on Mauna Loa) and to small networks on the summits of Kilauea and Mauna Loa. Many of the stations in the old trilateration network are now occupied with GPS, which supplanted EDM measurements in the 1990s. Our EDM instruments include two K&E Rangemaster III, one Ranger V, an AGA Model 8 Geodimeter helium-neon laser instrument, and one each HP 3808a and HP 3850a infrared laser instrument. We have an inventory of about 90 retro-reflector prisms, 10 high- precision altimeters, 6 thermistor units with Fluke 87 multimeter to record the resistance of the thermistor, and a number of tripods and optical tribrachs.

Seismology

See earthquake section for information about HVO's seismic studies.