Geodetic surveys measure the change in shape of our volcanoes due to changes in magma supply and storage. The USGS Hawaiian Volcano Observatory has a long history of using many different types of instruments and technologies over the decades to detect these changes.
GPS receivers are currently the primary instrument of choice to measure changes in distance and elevation due to movement of magma in and out of the volcanoes. These have replaced more traditional surveying instruments that were used in the past.
These measurements initially began as attempts to find the summit elevations and eventually led to the conclusion that Mauna Loa and Kilauea changed due to the coming and going of magma. HVO now operates 67 GPS stations on the Island of Hawaii that take elevation and position measurements constantly.
HVO also conducts campaign surveys to increase the coverage across Hawaiian volcanoes. Campaign GPS surveys are conducted periodically, where high precision instruments are deployed on the volcanoes and operate for days to weeks. These instruments are setup at long-term fixed sites, known as benchmarks, across both Kilauea and Mauna Loa. The sites are visited yearly, and the difference in position between each yearly visit provides information on how the volcano has changed or behaved over that period of time. Many of these benchmarks have been occupied every year since 1996, providing one of the longest spanning GPS time-series — a sequence of data points that occur over a period of time — of any volcano in the world.
These yearly campaign surveys help supplement the continuously recording GPS receivers that blanket the Island of Hawaii. Both the campaign and continuous GPS instruments can measure their positions to within a fraction of an inch, and can thereby detect extremely small movements on the earth’s crust. However, these continuous stations have significant infrastructure requirements, for example, substantial power consumption, radio telemetry needs, and site accessibility. Campaign GPS does not have the same requirements as continuous GPS. although the instruments are only deployed for a short time, the data they collect helps scientist to refine current models of volcanic activity, like inflation at the summit of Mauna Loa.
Kinematic GPS (kGPS) is another technique used to complement HVO’s continuous GPS network. The kGPS surveys take much less time to complete (a few minutes versus days). However, they rely on a static reference station to find a position and have significantly less precision (1 to 2 inches) than campaign GPS. HVO completes these surveys occasionally along Hilina Pali, Kanenuiohamo, and the summit of Kilauea.
This past May, HVO completed the Mauna Loa GPS campaign survey, visiting 32 sites across the volcano. along with Mauna Loa and Kilauea, HVO also surveys Hualalai and Haleakala every three to five years as part of our volcano monitoring program to keep a long-term record of the background deformation (“baseline”) of these quiet but still active volcanoes. Baselines are extremely important for potentially active volcanoes. The inactive periods of time help scientists create an accurate comparison point for when the volcano does become restless. To learn more about GPS read this Volcano Watch: https://www.usgs.gov/center-news/volcano-watch-important-point-measuring-volcanos-shape-high-precision-gnss.
The use of continuous and campaign GPS instruments together helps HVO scientists gain a better understanding of what might be occurring below the surface of our volcanoes and the time scale these changes take place. These measurements can reveal underground magma movement within the volcano, and have proved to be an essential tool in monitoring the internal conditions of the magmatic storage system.
Visit https://www.usgs.gov/observatories/hawaiian-volcano-observatory for past Volcano Watch articles, Kilauea and Mauna Loa updates, volcano photos, maps, recent earthquake info, and more. Email questions to askHVO@usgs.gov.
Volcano Watch is a weekly article and activity update written by U.S. Geological Survey Hawaiian Volcano Observatory scientists and affiliates.