Volcanic Ash Advisory Centers Research Articles

Volcanic plume above Mount St. Helens detected with GPS

Eruptions can produce not only flows of incandescent material along the slopes of a volcano but also ash plumes in the troposphere [Sparks et al., 1997] that can threaten aircraft flying in the vicinity [Fisher et al., 1997]. To protect aircraft, passengers, and crews, the International Civil Aviation Organization and the World Meteorological Organization created eight Volcanic Ash Advisory Centers (VAAC, http://www.ssd.noaa.gov/VAAC/vaac.html) around the globe with the goal of tracking volcanic plumes and releasing eruption alerts to airports, pilots, and companies. Currently, the VAAC monitoring system is based mostly on the monitoring systems of any local volcano observatories and on real‐time monitoring of data acquired by meteorological satellites.

Seismicity and tilt associated with the 2003 Anatahan eruption sequence

On May 10, 2003, the first historical eruption of Anatahan volcano in the western Pacific Mariana Islands was fortuitously recorded by a broadband seismograph installed on the island only 4 days prior to the eruption. This station, located 7 km WNW of the active crater, together with another broadband seismograph on Sarigan Island 45 km to the north, continued to operate throughout the 2-month period of major eruptive activity in May and June and throughout the majority of the following year. In June 2003, the Saipan Emergency Management Office and the US Geological Survey installed two telemetered high-gain short-period seismic stations to monitor the activity in real-time. The only earthquakes detected in the 4-day period from the initial seismograph installation until 6 h prior to the eruption occurred approximately 20 km to the northeast of the island on May 8. The first volcano-tectonic (VT) event located near the volcano occurred at 01:53 GMT on May 10. The number of events per hour then increased dramatically and a period of about 80 discrete earthquakes per hour commenced at about 06:20 GMT, immediately prior to the estimated eruption time of 07:30 from the Volcanic Ash Advisory Center. A long-period tilt signal recorded on the horizontal components of the broadband seismograph, indicating upward movement of the crater region, also commenced at about 06:20. Inflation continued until 09:30, when the direction of tilt reversed. Deflation continued until 17:50, coinciding with a reduction in the number of VT events. The larger VT events were located with a linearized least-squares location algorithm. Magnitudes of located VT events on May 10 ranged from 2.0 to 3.2, but a period of larger VT events were recorded on May 11, with the largest M 4.2. After about 36 h of intense earthquake activity, the number of discrete VT events declined and was replaced by nearly continuous volcanic tremor for the next 6 weeks. Differing types of very long-period events may suggest complex non-destructive magmatic source mechanisms, persisting dominantly throughout the first 10 days of the initial eruption. Visual reports indicate that a small craggy dome extruded sometime between May 20 and June 5. From analogy with other volcanic dome extrusions, we believe the dome probably extruded just as the tremor amplitude decreased dramatically about May 24. This dome was then destroyed between June 13 and 14. Reduced displacement of the co-eruption tremor is estimated as approximately 40–80 cm 2, suggesting an eruption with a Volcanic Explosivity Index of about 3.

Volcanic-ash hazard to aviation during the 2003–2004 eruptive activity of Anatahan volcano, Commonwealth of the Northern Mariana Islands

Within the Commonwealth of the Northern Mariana Islands (CNMI), Anatahan is one of nine active subaerial volcanoes that pose hazards to major air-traffic routes from airborne volcanic ash. The 2003–2004 eruptive activity of Anatahan volcano affected the region's aviation operations for 3 days in May 2003. On the first day of the eruption (10 May 2003), two international flights from Saipan to Japan were cancelled, and several flights implemented ash-avoidance procedures. On 13 May 2003, a high-altitude flight through volcanic gas was reported, with no perceptible damage to the aircraft. TOMS and MODIS analysis of satellite data strongly suggests that no significant ash and only minor amounts of SO 2 were involved in the incident, consistent with crew observations. On 23 May 2003, airport operations were disrupted when tropical-cyclone winds dispersed ash to the south, dusting Saipan with light ashfall and causing flight cancellations there and at Guam 320 km south of the volcano. Operational (near-real-time) monitoring of ash clouds produced by Anatahan has been conducted since the first day of the eruption on 10 May 2003 by the Washington Volcanic Ash Advisory Center (VAAC). The VAAC was among the first groups outside of the immediate area of the volcano to detect and report on the unexpected eruption of Anatahan. After being contacted about an unusual cloud by National Weather Service forecasters in Guam at 1235 UTC on 10 May 2003, the VAAC analyzed GOES 9 images, confirming Anatahan as the likely source of an ash cloud and estimating that the eruption began at about 0730 UTC. The VAAC issued its first Volcanic Ash Advisory for Anatahan at 1300 UTC on 10 May 2003 more than 5 h after the start of the eruption, the delay reflecting the difficulty of detecting and confirming a surprise eruption at a remote volcano with no in situ real-time geophysical monitoring. The initial eruption plume reached 10.7–13.4 km (35,000–44,000 ft), well into jet cruise altitudes; thereafter, the maximum plume height decreased and during the rest of the eruption usually did not exceed ∼5 km (∼17,000 ft), which lessened the potential hazard to aircraft at higher cruise altitudes. Drifting ash clouds commonly extended hundreds of kilometers from the volcano, occasionally as far west as the Philippines. Over the course of the eruptive activity in 2003–2004, the VAAC issued 323 advisories (168 with graphical depictions of ash clouds) for Anatahan, serving as a reliable source of ash-cloud information for aviation-related meteorological offices and air carriers. With a record of frequent eruptions in the CNMI, continued satellite and in situ real-time geophysical monitoring is needed at Anatahan and other Marianas volcanoes so that potential hazards to aviation from any future eruptive activity can be quickly and correctly assessed.

Acoustic surveillance for hazardous eruptions (ASHE)

The potential of using infrasound to rapidly identify explosive volcanic eruptions has been discussed in the environmental acoustics and aviation safety communities for some time. The ability of sounds in the 0.01–10 Hz range to propagate for long distances with little attenuation suggests broad-area regional monitoring with a modest number of observing sites is possible. The ASHE experiment tests both the practical utility of infrasound as a regional-scale volcanic eruption detection tool, and the feasibility of using such an infrasound system to provide timely operational alerts to aviation through Volcanic Ash Advisory Centres (VAACs). Several infrasound arrays are deployed in a volcanic region, sending data in real time to a central detector, and onward to participating VAACs for comparison with existing warning systems. The ASHE experiment will determine if infrasound can complement both seismic and satellite observations to improve monitoring of volcanic hazard. Continuous acoustic surveillance can reduce the ambiguity between eruptive and purely seismic activity in an active volcano and provide additional estimates for the onset time of an eruption. The onset time estimates can be used as triggers for ash transport models.

Observing the historic eruption of northern Mariana Islands volcano

Anatahan volcano erupted for the first time in recorded history at about 7:30 GMT on 10 May 2003, covering the island of Anatahan, in the Commonwealth of the Northern Mariana Islands (CNMI), with ash, and providing scientists with important opportunities to study this volcano. The eruption was first reported by the National Oceanic and Atmospheric Administration's Volcanic Ash Advisory Center at 12:32 GMT, based on satellite images of the ash cloud. At about the same time, unusual light flares were observed from an approaching small ship, the Super Emerald, which was carrying a group of seismologists from Washington University in St. Louis, Scripps Institution of Oceanography, and the CNMI Emergency Management Office. As morning broke, the ship was approximately 10 km from the island, and those on board witnessed billowing ash and gas rise from the volcano's caldera to form a great cloud exceeding 6 km in altitude (Figure 1).The scientists were in the region installing land seismographs for the Mariana Subduction Factory Imaging Experiment, a joint U.S. Japanese deployment of 20 land broadband seismographs and 58 ocean bottom seismographs funded (on the U.S. side) by the Margins program of the National Science Foundation. The experiment has the goal of imaging the magma production regions and mantle flow patterns within the upper mantle beneath the Mariana arc and backarc (see http://epsc.wustl.edu/seismology/MARIANA).

The application of AVHRR data for the detection of volcanic ash in a Volcanic Ash Advisory Centre

AbstractA volcanic ash detection product using AVHRR data has been developed for use in the London Volcanic Ash Advisory Centre, operated by forecasters at the Met Office. The product is an image that shows the brightness temperature difference between two infrared channels, which can be used to discriminate between clouds containing volcanic ash particles and those containing water droplets or ice crystals. Factors such as water vapour, water droplet and ice crystal content, opacity, cloud top temperature, ash particle size, surface emissivity properties and instrumental effects all have an effect on the spectral signal represented in the image. AVHRR imagery has been used to study the volcanic clouds ejected from eruptions of Mount Etna (Italy) in July 2001, Hekla (Iceland) in February 2000 and Mount Spurr (USA) in September 1992 to demonstrate the application of this product during volcanic events. The volcanic ash detection product provides essential information that can help forecasters locate volcanic ash and give appropriate guidance through advisory statements to the aviation industry and thus help avoid dangerous and expensive encounters between aircraft and volcanic ash. Copyright © 2003 Royal Meteorological Society.

Improved detection of airborne volcanic ash using multispectral infrared satellite data

A technique for improved detection of airborne volcanic ash has been developed that uses three infrared (IR) bands from meteorological satellites. The three IR bands are centered near 3.9, 10.7, and 12.0 μm wavelength. The technique is based on the sum of two brightness temperature differences (BTDs), scaled to maximize the brightness and contrast of volcanic ash in the output image. The physical effects attributed to the observed BTDs that help distinguish the volcanic ash from various meteorological cloud types are (1) differential absorption by volcanic ash or sulfur dioxide at 3.9 μm, 10.7 μm, and 12.0 μm and (2) strong solar reflectance by ash at 3.9 μm, which varies diurnally. On the basis of two examples using data from the Geostationary Operational Environmental Satellite (GOES) the three‐band IR technique is shown to provide better discrimination of volcanic ash from meteorological clouds than is possible using existing two‐band methods. This conclusion is supported by comparisons of brightness count profiles and estimation of false ash detection rate statistics. The best results from the three‐band IR technique are obtained during daylight hours over any surface, and at night when the ash cloud is over the ocean or other large body of water. The three‐band IR technique is one of the tools currently being employed operationally at the Washington Volcanic Ash Advisory Center.

Airborne Asian Dust: Case Study of Long-Range Transport and Implications for the Detection of Volcanic Ash

Abstract The transport of fine-grained Asian dust from its source (e.g., the Gobi Desert, Mongolia) to North America is a common springtime phenomenon. Because of its chemical composition (silicon, iron, aluminum, and calcium) and its particle size distribution (mean aerodynamic diameter 2–4 μm), Asian dust produces a negative signal in the split-window T4 − T5 algorithm, as does airborne volcanic ash. The split-window algorithm is commonly used by operational volcanic ash advisory centers. Thus, it is important to find ways to differentiate between airborne Asian dust and airborne volcanic ash. Use of Total Ozone Mapping Spectrometer aerosol and sulfur dioxide indices, in conjunction with the split-window method, can mitigate the possibility of a false airborne volcanic ash alarm. Asian dust also is important for other reasons. Thus, meteorological agencies should monitor it because 1) it can be transported thousands of kilometers from its source region and thus is of global interest (e.g., effects on ra...