Volcano Watch: New instrument measures lava lake with laser

  • Continuous Laser Rangefinder gauge on crater rim measures Halema’uma’u lava lake at Kilauea Volcano’s summit on Dec. 26. Exploded drawing of instrument optical enclosure is shown at upper right. (USGS photo and drawing by F. Younger/Special to West Hawaii Today)

Eyewitnesses drawn to the crater rim were excited, reverent, and watchful. The eruption onset was observed near and far via technology. The USGS Hawaiian Volcano Observatory (HVO) was onsite and online, transmitting scientific information as the eruption response mounted.

Kilauea’s volcanic activity requires the best available data in real time. HVO quickly deployed eruption response instruments to the field. New technology was implemented, leveraging the strength of HVO’s permanent volcano monitoring network.

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HVO’s prototype Continuous Laser Rangefinder (CLR) gauge was hardened for continuous gauging and pressed into service as part of this effort on Dec. 26. The data stream was fully networked and operational on January 8th, 2021.

This newly-developed instrument monitors lava lake dynamics with unprecedented resolution. The CLR gauge autonomously measures lava lake elevation in real time, using the light-reflecting properties of the lava surface.

The CLR gauge is stationed on the western rim of Halemaʻumaʻu crater within a closed area of Hawaiʻi Volcanoes National Park, under a National Park Service permit. The instrument is aimed into the crater at an inclination of 32.57 degrees below the horizon. Current measurement range is about 2,405 feet.

The CLR gauge transmits a laser pulse every second. The 1550 nanometer wavelength laser is invisible and eye safe. The laser beam broadens with distance, making a target footprint about 1.6 feet diameter on the lava lake surface near the previously active vents on Halemaʻumaʻu’s northwest wall.

A receiver diode senses laser signals reflected from down range. A microprocessor calculates the distance to the lake surface within a centimeter (less than ½ inch) by measuring the time of flight of the laser pulse.

An onboard inclinometer measures the slant angle of the laser beam. The beam angle is used to calculate vertical elevation of the lake surface below the surveyed instrument elevation. The instrument is stabilized by a sturdy tripod installation, a feature that improves measurement precision.

Real time range measurements are telemetered via HVO’s digital radio network. Database acquisition scripting and custom web plots were designed by HVO to make the lava lake gauge data useful and available on an HVO public webpage for the eruption.

Foul weather and gas emissions can produce error returns, which are mostly filtered out by minimum distance thresholds. Three discrete signal returns are processed, making good measurements possible in challenging conditions such as heavy rain and vog.

Kilauea is a harsh environment for instrumentation. Corrosive volcanic gas, abrasive tephra, heavy rainfall, lightening, and ballistic ejections are a threat to monitoring equipment. The CLR gauge optical components are protected by a custom enclosure. HVO designed 23 custom parts for the CLR gauge that were modeled with computer-aided design (CAD) software, 3D printed and machined in-house.

The CLR gauge is co-located with the KW optical camera and F1 thermal camera. The equipment is solar powered by HVO’s flyaway photovoltaic stations, which are rapidly deployed by helicopter. The laser instrument draws 4.5 watts power.

The CLR gauge complements other types of data routinely collected by HVO scientists in the field. Portable laser rangefinder measurements, photogrammetry modeling, and scanning Light Detection and Ranging (LiDAR) surveys are undertaken to study the lava lake at periodic intervals. These techniques provide broader spatial coverage than the CLR’s single point measurement, but are sporadic and have higher error.

Kilauea’s latest eruption inspired this innovation, and it has provided five months of high-resolution data documenting Halemaumau’s lava lake growth.

CLR lava lake measurements were combined with digital elevation maps of the crater to estimate effusion rate in real time, a first for Kilauea. The CLR was also instrumental in determining when the eruption paused. This resilient tool will certainly find wider applications in volcano monitoring in Hawaii and elsewhere.

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.

Volcano Activity Updates

Kilauea Volcano is not erupting. Its USGS Volcano Alert level is at ADVISORY (https://www.usgs.gov/natural-hazards/volcano-hazards/about-alert-levels). Kilauea updates are issued weekly.

Lava supply to the Halemaʻumaʻu lava lake has ceased and sulfur dioxide emissions have decreased to near pre-eruption background levels. Summit tiltmeters recorded one deflation-inflation cycle over the past week, with mild inflation over the past several days. Seismicity remains stable overall, with earthquake counts and tremor over the past week similar to the previous week. There are currently no indications suggesting that a resumption of volcanic activity is imminent. Kilauea remains an active volcano and future eruptions are possible at the summit or elsewhere on the volcano. For more information on current monitoring of Kilauea Volcano, see https://www.usgs.gov/volcanoes/kilauea/monitoring.

Mauna Loa is not erupting and remains at Volcano Alert Level ADVISORY. This alert level does not mean that an eruption is imminent or that progression to an eruption from the current level of unrest is certain. Mauna Loa updates are issued weekly.

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This past week, about 195 small-magnitude earthquakes were recorded below Mauna Loa. GPS measurements show low rates of deformation in the summit region over the past week. Gas concentrations and fumarole temperatures at both the summit and at Sulphur Cone on the Southwest Rift Zone remain stable. Webcams show no changes to the landscape. For more information on current monitoring of Mauna Loa Volcano, see: https://www.usgs.gov/volcanoes/mauna-loa/monitoring.

There were two events with three or more felt reports in the Hawaiian Islands during the past week: a magnitude-3.5 earthquake 2 miles east-northeast of Pahala on June 16 at 1:56 p.m. and a magnitude-3.7 earthquake 8 miles south of Volcano on June 12 at 3:19 p.m.

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