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Cascade Range Weekly Update
Friday, August 18, 2017 8:46 AM US/Pacific
Current Volcano Alert Level: NORMAL
Current Aviation Color Code: GREEN
Cascades Volcano Observatory's mission
The U.S. Geological Survey's Cascades Volcano Observatory strives to serve the national interest by helping people to live knowledgeably and safely with volcanoes in WA, OR, and ID.

HOT STUFF   (archive)
Young Volcanoes in WA, OR & ID1

You are invited to the OMSI Science Pub "Nature's Fury" on August 15.
July 25, 2017

On August 15, 2017, join us at the Oregon Museum of Science and Industry (Portland) for the evening Science Pub program "Nature's Fury: Living with Active Volcanoes."

Three renowned scientists, John Ewert (USGS-Cascades Volcano Observatory), Marta Calvache (Colombian Geological Survey) and Richie Robertson (University of West Indies), will share their experiences studying and responding to volcanic eruptions. Hear how advances in volcano science and lessons learned are applied globally and at our Cascade volcanoes.

This event is presented by the Oregon Museum of Science and Industry, U.S. Geological Survey, USGS-U.S. Agency for International Development, Office of U.S. Foreign Disaster Assistance, Volcano Disaster Assistance Program, U.S. Forest Service, and the Mount St. Helens Institute. Details are available at OMSI.

Field trip guide examines obsidian-rich lava flows in Oregon and California.
July 24, 2017

Obsidian-rich lava flows have been of interest to geologists, archaeologists, pumice miners, and rock hounds for more than a century. But active rhyolitic obsidian lava flows have never been scientifically witnessed and lively debate ensues at outcrops over the formation of some lava flow features.

At first glance, the surface of an obsidian flow appears to be a chaotic mixture of blocks, spines and hillocks of different colors, sizes, densities, crystallinity and vesicularity. However, on aerial photos (or after one stumbles around for a few hours), patterns begin to emerge. Folds and ridges are caused by flow-parallel compression. Three main textures appear on the flow front—finely vesicular pumice carapace, dense obsidian and coarsely vesicular pumice.

This new field guide takes you to locations at Newberry, South Sister and Medicine Lake Volcanoes, to examine the textural and structural characteristics of silicic lava flows. Download Emplacement of Holocene silicic lava flows and domes at Newberry, South Sister, and Medicine Lake volcanoes, California and Oregon for your next journey to central Oregon and northern California.

The field guide was developed for the August 2017 International Association of Volcanology and Chemistry of the Earth's Interior (IAVCEI) Scientific Assembly in Portland, Oregon.

New field guide explores pyroclastic density current deposits from the May 18, 1980, eruption of Mount St. Helens.
July 07, 2017

On the afternoon of May 18, 1980, pyroclastic density currents (PDCs) spilled over the crater rim and poured through the breach created in Mount St. Helens' north flank. At times, the PDCs collided, scoured and filled channels, laid down beds 40 feet (12 m) thick and traveled as much as 5 miles (8 km) from the vent.

Our ability to interpret the deposits is critical for understanding transport and depositional processes that control PDC dynamics—one of the most dangerous phenomena associated with explosive volcanism. The results of extensive work on the May 18, 1980, PDC deposits show that slope and irregular topography strongly influence PDC flow path, dynamics, criticality (for example, supercritical versus subcritical), carrying capacity, and erosive capacity. However, the influence of these conditions on ultimate flow runout and damage potential warrants further exploration through the combination of field, experimental, and numerical approaches.

This field guide describes the PDC deposits at Mount St. Helens and poses questions for further research. Download Field-trip guide for exploring pyroclastic density current deposits from the May 18, 1980, eruption of Mount St. Helens, Washington to learn more.

The field guide was developed for the August 2017 International Association of Volcanology and Chemistry of the Earth's Interior (IAVCEI) Scientific Assembly in Portland, Oregon.

Field trip guide examines Ohanapecosh and Wildcat Creek deposits near Mount Rainier.
June 29, 2017

Partly situated in Mount Rainier National Park, this field trip guide visits exceptional examples of volcaniclastic successions laid down in continental basins adjacent to the ancestral Cascades arc. The Ohanapecosh Formation (32–26 Ma) and the Wildcat Creek (27 Ma) beds record similar sedimentation processes from various volcanic sources. They show evidence of probable Surtseyan eruptions, tephra fallout over water, entrance of pyroclastic flows into water, scoria-cone building eruptions in shallow water, and resedimentation events. The field trip examines outcrops along White Pass, Cayuse Pass, Chinook Pass and at Burnt Mountain.

Download Field-Trip Guide to Subaqueous Volcaniclastic Facies in the Ancestral Cascades Arc in Southern Washington State—The Ohanapecosh Formation and Wildcat Creek Beds for your next road trip to this area.

The field guide was developed for the August 2017 International Association of Volcanology and Chemistry of the Earth's Interior (IAVCEI) Scientific Assembly in Portland, Oregon.

Explore Mount Hood with this new field trip guide.
June 26, 2017

Starting and ending in Portland, Oregon, this new field trip guide describes stops of geologic interest for a 175-mile adventure around the Mount Hood volcano.

Mount Hood is a 500,000-year-old composite volcano. Unlike Mount St. Helens, Mount Hood has not produced highly explosive eruptions. Rather, it has erupted andesite and (rarely) low-silica dacite lava flows and domes that have built the 11,241-feet-tall volcano. Pyroclastic flows triggered by the collapse of growing lava domes have generated lahars that swiftly melted snow and ice, as well as lahars generated by large landslides, that have surged tens of miles down valleys.

Use this guide to investigate the outcrops and unique features of Mount Hood, learning more about its history and how this active volcano may behave in the future. Download Field-trip guide to Mount Hood, Oregon, highlighting eruptive history and hazards and plan your next visit to the volcano.

The field guide was developed for the August 2017 International Association of Volcanology and Chemistry of the Earth's Interior (IAVCEI) Scientific Assembly in Portland, Oregon.

Seven-day field trip guide tracks the Columbia River Flood Basalts.
June 26, 2017

The Columbia River Basalt Group covers an area of more than 81,000 square miles. As the youngest continental flood-basalt province on Earth (16.7–5.5 Ma), it is well preserved, with a coherent and detailed stratigraphy exposed in the deep canyonlands of eastern Oregon and southeastern Washington.

This new field trip guide begins in southeastern Oregon near Burns, progresses northward into southeastern Washington, continues in the Pasco Basin and ends in the Columbia River Gorge near Stevenson, Washington. The excursions are arranged progressively from the oldest to the youngest units found in the heart of the flood-basalt source region. The road log examines the stratigraphic evolution, eruption history, and structure of the province through a field examination of the lavas, dikes, and pyroclastic rocks of the CRBs.

Download Field-trip guide to the vents, dikes, stratigraphy, and structure of the Columbia River Basalt Group, eastern Oregon and southeastern Washington and plan your summer trip.

The field guide was developed for the August 2017 International Association of Volcanology and Chemistry of the Earth's Interior (IAVCEI) Scientific Assembly in Portland, Oregon.

Deja Vu: Small Earthquake Swarm at Mount St. Helens Does Not Indicate Future Eruptive Activity
May 05, 2017

As many in the Pacific Northwest can attest to, the winter of 2017 has been a rough one.  Deep snow in the high country buried volcano monitoring sites and caused loss of telemetry and/or power. These problems reduced the Mount St. Helens seismic network, operated jointly by the Cascades Volcano Observatory (CVO) and the Pacific Northwest Seismic Network (PNSN), to roughly half its normal operating capacity. The consistently bad weather prevented CVO and PNSN staff from performing any mid-winter repairs.

A clear weather day on April 21, permitted CVO and PNSN personnel to visit Mount St. Helens and restore the seismic network to nearly full capacity. Immediately after repairs were made, the PNSN began locating small earthquakes at relatively high rates (1 earthquake every few hours) under Mount St. Helens. The damage to seismic stations reduced the ability of the seismic network to locate small-magnitude earthquakes, at least somewhat.

Further analysis has revealed that many of the earthquakes look similar to each other, a common feature of swarms at Mount St. Helens and a sign that the events are occurring in close proximity.  Using data from stations operable all winter, CVO scientists used the repeating characteristic of the earthquakes located since April 21 to track down when the swarm started. The result? There is good evidence that the uptick began as early as April 16 and definitely was occurring as of April 18.

As of May 5, the PNSN has located 47 earthquakes near Mount St. Helens since the seismic network was restored on April 21. Utilizing the similarity of earthquakes, we can detect well over 100 earthquakes that are part of this swarm.  Most earthquakes have depths between sea level and 3 mi (5 km) below sea level (approximately 2-7 km below the surface).  This is consistent with depths of earthquakes occurring since 2008, which are thought to be in response to recharge in the magmatic system.  Earthquake rates, though relatively high compared to background, are still only 1 earthquake every few hours, a rate that is consistent with past small swarms since 2008.  All earthquakes are volcano tectonic in character (no detected low-frequency or long period earthquakes) and the maximum magnitude thus far is a M1.3.  There is no detectable deformation or gas signal associated with this swarm.

Similar swarms occurred at Mount St. Helens in March-May 2016 and November 2016.  Both swarms had repeating earthquakes, average rates of 1-2 earthquakes/hour, and most earthquakes with magnitude below M1.5. 

The similarity of swarms at Mount St. Helens leads us to believe that similar processes cause them, and they are likely tied to magma recharge first detected in 2008. However, pinpointing that exact process is difficult. Some possible mechanisms include a spontaneous release of brine from the pressurized magma chamber into the crust above, a pulse of magma into the magma reservoir that transferred stress into the crust above, or just the breakage of a new pathway of fluid flow that was previously blocked by precipitated minerals. There are several reasons why it is very unlikely that this swarm is a precursor to imminent eruptive activity at Mount St. Helens—it is similar to ones in the past that did not lead to surface activity; it consists of very small earthquakes occurring at relatively low rates; there are no other geophysical indicators (deformation, tilt, gas) of unrest.

Small magnitude earthquake swarms detected beneath Mount St. Helens.
December 12, 2016

Four swarms of small magnitude earthquakes were detected beneath Mount St. Helens beginning November 21, 2016. No anomalous gases or increases in ground inflation have been detected and there are no signs of an imminent eruption.

During a week's time, there have been over 120 tiny earthquakes, most too small to be formally located by the Pacific Northwest Seismic Network. The earthquakes are magnitudes 0.3 or less; the largest has been a magnitude 0.5. Most of the earthquakes are occurring in the shallow volcano plumbing system about 1-2 miles below sea level. These earthquakes are too small to be felt at the surface.

The current pattern of seismicity is similar to swarms most recently seen at Mount St. Helens in March-May 2016, and in 2014 and 2013. The magmatic system is likely imparting its own stresses on the crust around and above it, as the system slowly recharges. The stresses drive fluids through cracks, producing the small quakes. Subtle evidence of recharge has been observed since 2008 and can continue for many years. It is a sign that Mount St. Helens remains an active volcano.

For more information, see the Activity Updates for Volcanoes in CVO Area of Responsibility and Earthquake Monitoring at Mount St. Helens.

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