Volcano Watch — New Monitoring Instruments at Mount Rainier Have Their Roots in HVO's History

Rainier is the third largest of Cascade Range volcanoes and the highest peak in Washington state (4,392 m, 14,410 ft). Its slopes pack more snow and ice than any other volcano within the lower 48 states.

Mount Rainier has the added hazard of having shed huge lahars (slurries of mud and boulders) into surrounding valleys during the past few thousand years. These events, which begin as large landslides, may be unrelated to volcanism, because they can originate simply by failure of weak, clay-altered rock in the volcano's core. Similar large landslides today would be costly to infrastructure and deadly to many living in communities as far west as Tacoma, 80 km (50 miles) distant. About 80,000 people and their homes are at risk in Mount Rainier's lahar-hazard zones.

The monitoring sites installed recently are located at Observation Rock, on the volcano's north flank, and St. Andrews Rock, high on the west flank. The installations include tools well known to followers of Hawaiian volcanism. For example, each site has a seismometer to track small earthquakes that might occur at shallow depths within the volcano. Additionally, the seismometer at Observation Rock is capable of recording across a broader frequency range (or longer period), which makes it useful to better understand the source and energy of low-frequency, as well as larger, earthquakes. Such "broadband" seismometers play an increasingly important role in modern seismologic interpretation.

Each site hosts a continuously operating GPS receiver. This instrument consists of an antenna mounted on a mast, from which it receives signals from satellites within its line of sight. The resulting data allow pinpoint positioning, as accurate as a few millimeters (a tenth of an inch or so). The goal is to track changes resulting from incipient landsliding or volcanic deformation.

Our wintertime experience at Mount St. Helens has taught us that GPS antennae deflect slightly as snow and ice build on them, leading to shifting positions that have nothing to do with landslide or volcanic hazards. To master this shortcoming, we needed a second tool sheltered from, and unaffected by, winter weather. Therefore a borehole tiltmeter was added to each of the new Mount Rainier monitoring sites.

Each tiltmeter, about the length and diameter of an adult's arm, is placed vertically about 3 m (10 ft) deep, to shield it from the surficial effects of day/night warming and freezing. The instrument is remarkably sensitive, recording in units of angular rotation known as microradians. One microradian (0.000057 of a degree) is the amount of tilt that results if a board 1 km long were displaced at one end by only a dime's thickness. Modern tiltmeters are 10 to 100 times more precise. In the dime-beneath-board analogy, we must sliver the dime to visualize the precision of the tiltmeter.

Those familiar with Mount Rainier will realize that these two new installations were a substantial undertaking. The sites are in roadless areas, so equipment was flown in by helicopter. The data from each site must be collected and radioed to stations 50-100 km (30-60 mi) distant and then relayed to the corresponding seismic or volcano observatory. Solar panels and batteries maintain operation through prolonged stormy weather. Each installation was built to withstand substantial snow load and high winds.

Volcano monitoring is a business of experimentation, of trial and error. Much of its modern instrumentation has its roots at the Hawaiian Volcano Observatory and the work conducted there since the early 20th century. The new Mount Rainier sites include well-known workhorses, like seismometers, but also tools that have become common in only the past decade, like GPS receivers and borehole tiltmeters. At the heart of these experiments lies the goal of warning the populace when nearby volcanoes become restless.

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Volcano Activity Update

Kīlauea Volcano continues to be active. A vent in Halema`uma`u Crater is erupting elevated amounts of sulfur dioxide gas and very small amounts of ash. Resulting high concentrations of sulfur dioxide in downwind air have closed the south part of Kīlauea caldera and produced occasional air quality alerts in more distant areas, such as Pahala and communities adjacent to Hawai`i Volcanoes National Park, during kona wind periods. On September 5, scientists observed a 50-m - (160 ft) diameter lava lake about 100 m (330 ft) below the vent rim on the floor of Halema`uma`u; the lava cannot be seen from the rim of Halema`uma`u Crater or Jaggar Museum Overlook. There have been several small ash-emission events from the vent, lasting only minutes, in the last week.

Pu`u `Ō`ō continues to produce sulfur dioxide at even higher rates than the vent in Halema`uma`u Crater. Trade winds tend to pool these emissions along the West Hawai`i coast, while Kona winds blow these emissions into communities to the north, such as Mountain View, Volcano, and Hilo.

Lava continues to erupt from fissure D of the July 21, 2007, eruption and flows toward the ocean through a well-established lava tube. A small, short-lived breakout, probably near the ocean entry delta, was active on Monday, September 15; otherwise, no significant surface flows have been observed this past week. Lava continues to flow into the ocean at Waikupanaha.

Be aware that active lava deltas can collapse at any time, potentially generating large explosions. This may be especially true during times of rapidly changing lava supply conditions. Do not venture onto the lava deltas. Even the intervening beaches are susceptible to large waves generated during delta collapse; avoid these beaches. In addition, steam plumes rising from ocean entries are highly acidic and laced with glass particles. Check Civil Defense Web site or call 961-8093 for viewing hours.

Mauna Loa is not erupting. Two earthquakes were located beneath the summit this past week. Continuing extension between locations spanning the summit indicates slow inflation of the volcano.

Three earthquakes beneath Hawai`i Island were reported felt within the past week. A magnitude-2.1 earthquake occurred at 12:02 p.m., H.s.t., on Friday, September 12, 2008, and was located 6 km (4 miles) southwest of Holualoa, at a depth of 9 km (5 miles). A magnitude-3.1 earthquake occurred at 4:57 p.m. on Monday, September 15, 2008, and was located 14 km (9 miles) northwest of Kailua at a depth of 11 km (7 miles). A magnitude-2.2 earthquake occurred at 1:51 p.m. on Wednesday, September 17, 2008, and was located 2 km (1 mile) north of Ka`ena Point at a depth of 8 km (5 miles).

Visit our Web site for daily Kīlauea eruption updates, a summary of volcanic events over the past year, and nearly real-time Hawai`i earthquake information. Kīlauea daily update summaries are also available by phone at (808) 967-8862. Questions can be emailed to askHVO@usgs.gov. skip past bottom navigational bar