More people were probably killed by the 1790 eruption of Kīlauea than by any other eruption in what is now the United States. The deaths apparently occurred along a trail crossing the northwest flank of Kīlauea near Nāmakanipaio, when a ground-hugging surge of hot steam and rocks swept across the ground at high speed. Wet volcanic ash fell just before the lethal surge, and several hundred people left footprints in the ash beyond the limit of the surge. A field study to understand better the tragic events was made several years ago. This study identified most, or all, of the deposits left by the 1790 eruption and interpreted the kinds of explosions responsible for the deposits. Three main explosions took place within hours, perhaps minutes, of each other. The first main explosion ejected wet ash that was transported southwestward by the trade wind. This ash deposit now contains the footprints of mainly women and children (as determined by foot size), southwest of the summit. The next explosion was the largest. Its column of ash rose 12–15 km (40,000–50,000 ft) above the volcano as interpreted from physical characteristics of the deposit, and notes from marooned sailor John Young in Kawaihae. The third explosion produced the lethal surge that sped across the summit’s western flank. The falling hot debris hit the ground and surged downslope, trapping people on the trail. What caused the explosions? For years geologists assumed that groundwater heated to steam powered them but there isn't clear evidence of this. Another possibility is that gas leaving magma was trapped underground briefly, pressurizing and finally bursting out. Or perhaps a part of the caldera collapsed in 1790. With all we’ve learned, there’s a long way to go to understand completely Kilauea’s most lethal eruption. But one thing is clear: large explosions can happen again. Shown in the photo, are footprints made in muddy ash during #Kilauea's 1790 eruption. Several hundred, and possibly more than a few thousand, people were killed by the eruption soon after the footprints were made. #HawaiianVolcanoObservatory #HVO #USGS #Kilauea #VolcanoWatch

In recent weeks, Hawaiian Volcano Observatory geophysicists have been undertaking a Global Positioning System (GPS) campaign across Kīlauea. As shown in the photo, an HVO geophysicist is leveling and centering one of the survey tripods over a benchmark southwest of Halema‘uma‘u in the Ka‘ū Desert. During a GPS campaign—which is completed annually—scientists temporarily deploy a number of GPS instruments at established benchmarks. The recorded positions are compared with those from previous years to discern subtle patterns of ground deformation associated with volcanic activity. These data augment the permanent, continuously recording GPS instruments in HVO's monitoring network. USGS image taken August 6, 2021. #USGS #HVO #HawaiianVolcanoObservatory #Kilauea #GPS

Did you read the article in EOS, “Don’t Call It a Supervolcano” (http://ow.ly/p74U50FPlBH)? Scientists with the Yellowstone Volcano Observatory made really great points: It’s not a supervolcano. In its 2.2-million-year history, the Yellowstone caldera system has erupted catastrophically only 3 times. Yellowstone is not going to erupt again anytime soon, but when it does, it’s much more likely to produce a lava flow than an explosive event. While some lava flows have been hundreds of feet thick, they are impressive but not particularly hazardous beyond the immediate area. The system isn’t primed and ready to erupt. Currently, the two stacked magma chambers under Yellowstone are mostly stagnant. The magma reservoirs contain between 5% and 15% molten material and you need at least 50% for it to mobilize and begin moving toward the surface. Unrest won’t take anyone by surprise. The process of filling a magma chamber with molten material is not a quiet one. There would be increased seismicity, ground deformation, changes in thermal and gas emissions for decades and perhaps centuries in advance of an eruption. Few changes go undetected. The Yellowstone caldera is one of the best-monitored volcanoes on Earth. Satellites keep an eye on the seasonal cycles of ground deformation, while thermal and gas monitoring networks detect subtle changes in heat and gas outputs. Dozens of permanent and hundreds of portable seismic stations spread throughout the park and around its borders keep tabs on Yellowstone’s earthquakes and earthquake swarms. The swarms are usually triggered by water moving underground in geothermal areas. What hazards should you expect at Yellowstone? The most likely geologic hazard to affect park visitors is a hydrothermal explosion. The next most likely hazard is a large earthquake. View of Obsidian Cliff, a thick rhyolite lava flow that erupted about 180,000 years ago. USGS photo taken June 20, 2001 by S. Brantley.

Why study geysers? • Similar to volcanoes, geysers are transient features with periods of activity and dormancy. Because geysers have smaller eruptions and erupt more frequently than volcanoes, they provide useful natural laboratories to study eruption processes and test new monitoring technologies. • Eruptions at geysers and volcanoes are controlled by delicate balances in heat supply and gas and fluid flows within their systems, and by the tortuous pathways that liquid water, steam, and magma take to the surface. Studying physical controls on geyser location, longevity, and eruption intervals can improve our understanding of interactions between Earth’s interior and surface environment. • Natural geysers are rare—fewer than a thousand exist today worldwide. About half of Earth’s geysers are located in Yellowstone National Park. Other large geyser fields are in the Valley of Geysers in the Kamchatka Peninsula of Russia, El Tatio in Chile, and Geyser Flat at Te Puia, Rotorua, in New Zealand. They deserve both our wonder and our protection. Read the full article (“Why Study Geysers”) in EOS: http://ow.ly/B6wg50FPloQ. The photo is Steamboat Geyser, in Yellowstone National Park.

Welcome back to #OneOnOneWednesday! I am Natalea Cohen and today I am interviewing Kleinman Awardee Jackie Giblin. Jackie is a PhD student at #ArizonaStateUniversity. Q: What are you working on? I am investigating the post-caldera magmatic plumbing dynamics of the resurgent caldera, Valles Caldera, in New Mexico. I am specifically studying the eruption characteristics of the El Cajete pumice fall unit, which is about 50,000 years old and the most recent explosive deposit. Q: Why is it important to do this? The most recent volcanic deposits of Valles Caldera, including El Cajete, are compositionally distinct from previous eruptions which occurred 1.2 and 0.5 million years ago; indicating a potential new magmatic cycle at Valles. Although another caldera-forming eruption is highly unlikely, the most recent explosive units at Valles may provide critical insight into future eruptions of similar magnitude as well as the hazards associated with this type of magmatic resurgence. Q: Why does this interest you? So much of geology operates on really long timescales, which can be hard to appreciate from the human perspective. Volcanic events are some of Earth’s most violent and dynamic processes which can occur in real time and have devastating impacts to life on this planet. Studying volcanoes is not only a fascinating display of the power within Earth but imperative in protecting present and future generations from volcanic hazards. Q: What is your ultimate goal? I am really passionate about science communication and getting people excited about the geosciences. I would love to end up in a research position where I can continue that. Q: If you could travel anywhere, where would it be and why? Iceland- not only does it have active volcanism but is the only place in the world where you can swim directly in between two tectonic plates! Q: Great photo! What were you doing? I am enjoying Arizona’s San Francisco volcanic field, home to over 600 cinder cones! Thanks Jackie! Good luck with your research.

Monitored CALIFORNIA VOLCANOES Current Volcano Alert Level: all NORMAL Current Aviation Color Code: all GREEN Start planning your next road trip with insight from field trip guides like this one for the #Lassen segment of the Cascade Arc. Find where basalt flowed into an ancestral lake to form pillows, the best sites for panoramic views, where to see fumaroles and mudpots, and how Bumpass Hell got its name. Self-directed field trip guides provide background on volcanism, notable events, and places where you can stop and learn more. A list of downloadable field trip guides for areas of the West is available by searching "Field-trip guides to selected volcanoes and volcanic landscapes of the western United States" (http://ow.ly/gTKT50FOwYp). Additional information may be available from your state geological survey. Activity Update: All volcanoes monitored by #CalVO using telemetered, real-time sensor networks exhibit normal levels of background seismicity and deformation. These include Mount Shasta, Medicine Lake Volcano, Clear Lake Volcanic Field, Lassen Volcanic Center, Long Valley Volcanic Region, Coso Volcanic Field, Ubehebe Craters, and Salton Buttes. Seismicity: • Clear Lake Volcanic Field: One earthquake measuring M2.3. As is typical, moderate levels of seismicity were recorded at the Geysers geothermal steam field; 33 earthquakes at or above M1.0 were detected, the largest a M2.0. • Lassen Volcanic Center: Two earthquakes at or above M1.0 were detected, the largest a M2.7. • Long Valley Volcanic Region: No earthquakes at or above M1.0. As is typical, moderate levels of seismicity were observed south of the caldera in the Sierra Nevada range; 7 earthquakes at or above M1.0 were detected, the largest a M2.6. •Mount Shasta, Medicine Lake, Ubehebe Craters: No earthquakes at or above M1.0. •Coso Volcanic Field: One earthquake detected, a M1.0. •Salton Buttes: Two earthquakes at or above M1.0 were detected, the largest a M1.8. Earthquake counts are preliminary and subject to change after review by seismologists. #USGS #CaliforniaVolcanoObservatory #VolcanoUpdate

A boring gray rock? Hardly. Just take a closer look. Thin slices of polished volcanic rock provide a wealth of information about what's going on in the magmatic plumbing system and the conditions of magma ascent. This is a polished mount backscatter electron image of a breadcrust bomb erupted from Great Sitkin Volcano (Alaska) on May 25, 2021. The image 8.2 x 7.4 mm across. The top of the image captures the dense rind of a bomb while the vesicular interior is exposed along the bottom. Mineral phases include plagioclase (dark gray), pyroxenes (medium gray) and magnetite (white). Void spaces and vesicles are black. Rhyolitic glass forms interstitial spaces between mineral grains and is similar color to plagioclase. Trace amounts of apatite (light gray) and an SiO2 phase (dark gray and anhedral) are also visible. Elevated surface temperatures and small earthquakes were detected over the past day at Great Sitkin consistent with continued growth of a lava dome. No explosions or ash emissions were detected. A clear, high-resolution satellite image from Friday August 6 showed growth of a circular lava dome over 300 m in diameter. Information about Great Sitkin and Alaska volcanoes is available on the Alaska Volcano Observatory webpage http://ow.ly/zp7R50FOu5J Image acquired on an JEOL 6510LV SEM at 20 kV, 12 mm working distance, spot size of 65, and in BEC imaging mode, on July 13, 2021 by M. Loewen (Alaska Volcano Observatory / U.S. Geological Survey).

The Shell Rock (SHRK) monitoring site is located on the northeast side of Mount Hood volcano in the Oregon Cascades. A GPS antenna is mounted to a pole and a seismometer is buried underground. The fiberglass enclosure houses power supply and communications equipment, and it's designed to withstand harsh weather. This week, field crews were out checking on GPS monitoring equipment around Mount Hood. Cascade Range volcanoes in Oregon and Washington are GREEN/NORMAL this week. http://ow.ly/TZRa50FMhFb Small earthquakes were located at Mount Rainier, Mount St. Helens, Mount Hood, Three Sisters, and Newberry, consistent with background activity at each volcano. #CVO

Welcome back to #OneOnOneWednesday! I’m Natalea Cohen and today I’m interviewing Kleinman Awardee Kate Hewitt. Kate is a PhD student at #UCDavis. Q: What are you working on? I’m investigating the most recent smaller eruptions at #Yellowstone. I look for small crystals within erupted lavas and use isotopes of lead measured in the small crystals to track variations in magma composition over time and space. Q: Why do you like what you do? I love that I get to travel to volcanic landscapes to collect samples, use highly precise geochemical techniques in the lab, and collaborate (and learn) from experts in different disciplines and different backgrounds. Q: What inspired you to do this? My inspiration comes from a deep curiosity about what triggers a volcano to erupt. Also, there are so many interesting techniques being used by top scientists to study volcanoes. It's truly jaw-dropping! Q: What is your ultimate goal? My ultimate goal is to work towards expanding global capabilities to understand and predict volcanic hazards. I would love to be part of missions like the #USGS #VolcanoDisasterAssistanceProgram. Research scientists contribute training, equipment, and expertise to countries worldwide that face volcanic hazards. Also, research scientists with VDAP get to work with research institutions, and emergency management agencies to develop new technologies and preparedness plans. In turn, we can continue expanding our knowledge of volcanoes here in the United States! Q: What is one thing you wish people knew about you? I didn’t start studying geology until my late 20’s! In fact, I was working towards my MS in Management when I decided to visit the geology department at my school. I was instantly hooked! It was really hard work to start studying science from scratch. There was a lot of self-doubt and fear in taking such a leap. But it was so worth it. My younger self would have never imagined that I would be pursuing a PhD let alone to study volcanoes. Q: Great photo! What were you doing? I am using a centrifuge to separate clay minerals. We used these samples to determine a more precise age of Miocene volcanic deposits in Ankara, Turkey. Thanks Kate!

All volcanoes in California have been at normal background levels of activity in the past week. http://ow.ly/b6Oe50FJEqv (Scroll down for details) Did you know that there's an ancient volcano hiding in a Bay Area park? If you've ever been to the Sibley Regional Volcanic Preserve in the Berkeley Hills, you've been walking through a 10-million-year old collection of basalt lava flows, dikes and sills, breccias, and tuffs. These rocks were thought to have erupted over a several-hundred-thousand-year period, many of them from the Round Top Mountain vent, and fossils found in some of the tuffs indicate that the area may have been wet or hosted pools of water between eruptions. Collectively, the volcanic rocks are known as the Moraga Formation. In this photo, a vent on northeast flank of Round Top is exposed by the abandoned sand and gravel quarry. One interesting feature of this volcanic area is that it's probably connected to a much larger volcanic field 80 miles to the south, known as the Quien Sabe Volcanic Field. The Berkeley and Quien Sabe fields were 'dismembered' by the motion of the Pacific tectonic plate, which dragged the Berkeley side northward along the Hayward-Calaveras Fault System. This plate motion is also visible to the south in the Pinnacles volcanic center, where the 23-million-year-old volcanic rocks were displaced 195 miles from their 'birthplace' near Los Angeles. Learn more about these rocks in this Geologic Excursion: http://ow.ly/Jlo150FJEqy ------------------------------------------------------------ Recent observations: Earthquakes consistent with background activity were observed at the Clear Lake Volcanic Field, Mammoth Mountain, Salton Buttes, and the Coso Volcanic Field in the past week. Typical moderate levels of seismicity were present in the Sierra Nevada range south of the Long Valley Caldera and in the Geysers geothermal steam field south of Clear Lake.

This week, #CVO field crews were at Mount St. Helens to do station maintenance and equipment upgrades. The photo shows station GUAC on the north side of Mount St. Helens (near distance). Crater Glacier is visible in the middle distance (the ridge covered with darker rock at the opening of the crater), along with the lava domes in the center of the crater (far distance with some snow cover). One of the field teams focused on installation of an infrasound array. Infrasound is essentially a low-frequency microphone that detects acoustic waves at frequencies too low to be heard by humans (below 20 Hz). Any process that moves air in the atmosphere can produce infrasound. Wind is an extremely efficient generator of infrasound energy but for the volcano monitoring program, infrasound will be used for detecting explosions, rock fall, and avalanches. This week, all volcanoes in the Cascade Range of Washington and Oregon are at normal background levels of activity. Current Volcano Alert Level: NORMAL Current Aviation Color Code: GREEN Recent Observations: Over the past week small earthquakes were located at Mount Rainier, Mount St. Helens, and Mount Hood, consistent with background seismicity at each volcano. This week field crews worked at Mount St. Helens to perform maintenance and upgrades at several monitoring sites, at Newberry to perform maintenance at several stations and also to look for potential new monitoring station sites, and at Three Sisters to perform geological investigations. USGS image taken July 28, 2021 by C. Gabrielson. #CVO #CascadesVolcanoObservatory #MountStHelens #MSH #FieldphotoFriday

Radar isn’t just for meteorologist forecasting weather. Volcanologists use radar to study volcanic activity, which is the topic of this week’s #VolcanoWatch. Weather radar is an extremely important tool for studying explosive eruptions. Radar pulses reflecting off suspended ash, water droplets, or ice crystals in volcanic plumes provide insight into the plume’s composition and 3D structure. Doppler radar systems used to measure wind speed can also measure turbulence structures in plumes which allows us to track how they capture air, grow in size, and rise through the atmosphere. Using tens of scans per hour, we can measure plume and eruption evolution in time. This can aid in hazard assessment and eruption interpretation. The Island of Hawai‘i hosts two WSR-88D radar stations, at South Point (PHWA) and Kohala (PHKM). The December 20, 2020, eruption plume at Kīlauea volcano was visible to both stations, so their data help understand this interesting eruption. The water lake in Halema‘uma‘u was 50 m (164 ft) deep and growing when Kīlauea summit erupted on December 20, 2020. A new fissure opened above the lake on the crater wall at 9:30 pm. A large volume of lava spilled down into the lake, boiling the water, and producing a volcanic steam plume. The plume began rising immediately but slowly, reaching 13 km (43,000 ft) above sea level at its peak. By 11:00 p.m., HST, the water had vanished, replaced by a growing lava lake. Radar measurements of the plume were accessible minutes after the plume appeared and clearly show its development, increasing height, intensity, detachment and decline after the water lake dried. It shows that the plume pulsed, likely related to changes in lava effusion rates or lava-water contact area. Another advantage of weather radar is accessibility. Many stations provide free publicly available near-real-time data, accessible through the National Oceanic and Atmospheric Administration (NOAA) free Weather and Climate Toolkit software. So anyone can use the data! The graphic is an example of 2D and 3D radar visualization of the December 20, 2020, Kīlauea volcanic plume. #USGS #HVO #HawaiianVolcanoObservatory