Ka‘ū News Briefs, Saturday, November 7, 2020

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USING CUTTING EDGE TECHNIQUES TO MONITOR KĪLAUEA'S HOT WATER LAKE is the focus of this week's Volcano Watch, written by U.S. Geological Survey Hawaiian Volcano Observatory scientists and affiliates. This week's article is by HVO technician Frank Younger:
    Innovative Monitoring of Kīlauea's Summit Water Lake
    Famous for glowing red lava and billowing volcanic plumes, Halema‘uma‘u has long inspired poets, painters and photographers to find meaning in the color and light of this dynamic landscape.
    Today, Kīlauea's current phase of activity has inspired volcanologists to experiment with cutting edge techniques to understand the dynamic colors and patterns of Halema‘uma‘u’s newest feature: a steaming hot water lake.

An HVO scientist tests a colorimeter instrument on the water lake within Halema‘uma‘u, at Kīlauea's summit. Colorimetry is the measurement of the wavelength and intensity of light. USGS photo by M. Patrick

    For fifteen months now, hot groundwater has been seeping into the collapse pit created by the evacuation of the 2008–2018 Halema‘uma‘u lava lake and part of the underlying summit magma chamber. Since the gaping pit and the water lake rising within are physically inaccessible, the USGS HVO uses remote techniques to monitor this changing, and potentially hazardous, environment.
    HVO uses Unoccupied Aircraft Systems (UAS, or "drones") to collect water samples, the chemical analyses of which are snapshots of lake composition. Visual and thermal cameras keep constant watch on the lake surface and the hot fumaroles surrounding it. LiDAR (Light Detection and Ranging) helps to reveal the lake's growing form. A Digital Elevation Model (DEM) is integrated with frequent water level measurements to calculate lake depth, volume, and inflow rate. These quantitative data sets are complemented by the written accounts of HVO scientists, who document their first-hand observations in field logs.
    The lake gives strong impressions of color, pattern, and motion. When it first emerged, it was described as a pond of milky turquoise water. Later, it developed yellow hues and green shoreline margins. Today, the lake surface has lobes of rust orange water over expanses of deep brown, with patches of light brown and tan. Elongated green inflows emerge from the rocky shoreline, along which several ruddy spots have recently upwelled.
    The water surface is a mosaic in constant motion, a scene that changes by the minute and hour. Sharply defined color boundaries are often seen, accompanied by more subtle gradients and mixing. The patchwork waters may indicate zones of distinct temperature and dissolved constituents, and their movement is likely driven by differentials of density, wind, and fresh groundwater inflow. 

    As HVO scientists documented the lake's early growth and development, they recognized the need to define these valuable visual observations of color with quantitative measurements, and to help control for variable effects of lighting, personal impressions, and the color biases in cameras.  

The colorful caldera lake at Kīlauea summit. The view is from the western rim of Halema‘uma‘u crater, 1900 ft (580 m) above the water surface, in a restricted area of Hawai‘i Volcanoes National Park. USGS photo by M. Patrick on Aug. 25.

    A colorimeter instrument, a handheld optical device that measures chromaticity and brightness, is being field-tested for this purpose. A similar type of color measurement was conducted at Aso Volcano in Japan in 2010, inspiring the techniques used by HVO. In an experiment to test its efficacy at Kīlauea, HVO scientists use a portable colorimeter to quantify visual observations and track color changes over time.
    Colorimeters are more commonly used in industries like food processing and textile manufacturing than in volcanology. Colorimetry is the measurement of the wavelength and intensity of light. The quantification of color can be divided in two parts. Brightness, or luminicity, is the quantity of light that is reflected, emitted from, or passes through an object. Chromaticity is a measurement of hue and colorfulness, independent of brightness. Colorimetry relates these variables to the human eye's sensation of color, and to our judgement of the physical stimulus of light.
    In the field, scientists make broad visual observations, then sight the colorimeter at a point of interest. The record of chromaticity and brightness builds upon hydrologic and geologic data sets, contributing insight that may help link other remote observations. Analysis of the colorimetry data from this experimental technique may help scientists explain the dynamic colors seen at the Halema‘uma‘u lake.
    Lake color changes may possibly even signal changing volcanic conditions beneath the watery depths. Water color and appearance changes have been observed at other active crater lakes around the world. For example, at Aso Volcano in Japan in 2003, Yudamari lake changed from blue green to solid green before an eruption occurred at the lake bottom.
    While we don't know if the water lake within Halema‘uma‘u would have a similar color change prior to an eruption, it is a potential indicator that HVO scientists will be looking for and tracking as part of routine monitoring in the post-2018 collapse era of Kīlauea activity.

Discovered in July of 2019, the lake in Halema‘uma‘u began as a small, green pond. USGS photos

    Volcano Activity Updates
    Kīlauea Volcano is not erupting. Its USGS Volcano Alert level remains at NORMAL (https://www.usgs.gov/natural-hazards/volcano-hazards/about-alert-levels). Kīlauea updates are issued monthly.
    Kīlauea monitoring data for the month of October show variable but typical rates of seismicity and ground deformation, low rates of sulfur dioxide emissions, and only minor geologic changes since the end of eruptive activity in September 2018. The water lake at the bottom of Halema‘uma‘u continues to slowly expand and deepen. For the most current information on the lake, see https://www.usgs.gov/volcanoes/kilauea/k-lauea-summit-water-resources.
    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 eruption from current level of unrest is certain. Mauna Loa updates are issued weekly.
    This past week, about 42 small-magnitude earthquakes were recorded beneath the upper-elevations of Mauna Loa; most of these occurred at shallow depths of less than 8 kilometers (about 5 miles). Global Positioning System measurements show long-term slowly increasing summit inflation, consistent with magma supply to the volcano's shallow storage system. Gas concentrations and fumarole temperatures as measured at both Sulphur Cone and the summit 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 three events with three or more felt reports in the Hawaiian Islands during the past week: a M2.6 earthquake 6 km (3 mi) N of Wai‘ōhinu at 0 km (0 mi) depth on Nov. 3 at 6:40 a.m., a M3.5 earthquake 9 km (5 mi) ENE of Pāhala at 30 km (18 mi) depth on Nov. 2 at 1:47 a.m., and a M2.9 earthquake 1 km (0 mi) W of Pāhala at 34 km (21 mi) depth on Oct. 31 at 8:25 a.m.
    HVO continues to closely monitor both Kīlauea and Mauna Loa for any signs of increased activity.
    Visit HVO's website for past Volcano Watch articles, Kīlauea and Mauna Loa updates, volcano photos, maps, recent earthquake info, and more. Email questions to askHVO@usgs.gov.