William I Rose
8 February 1998
For more than two years the activity at Soufriere Hills, Montserrat has produced numerous ash-bearing volcanic clouds that drift around the Lesser Antilles region. The activity is a growing hazard beyond the island itself because volcanic clouds are a serious threat to aviation (Rose, 1986; Casadevall, 1994) and because in general the number and severity of the eruptions has been increasing (Young et al, 1997). Regular information about activity is provided by the BGS scientific team who monitors the volcano from the ground using seismic sensors, visual observations and other methods. Although ground based volcanic monitoring can detect eruptions, visual confirmation of an eruption and data on its intensity is not always possible within a few minutes time, especially during bad visibility periods which are quite common. Hazard to aircraft from volcanic cloud encounters is very serious and many encounters have happened only minutes to a few hours after eruptive events, so timely information on the eruption's onset and its intensity is vital. As shown from the activity of December 26, 1997, within 30 minutes a volcanic cloud can spread from Montserrat to cover neighboring islands.
To effectively mitigate volcanic cloud hazards within the busy flight lines of the Caribbean region, warning of eruptions is needed within a few minutes, 24 hours a day and in all weather conditions. Ground-based observations have limited utility for assessing volcanic clouds. Aircraft observations also have limited value, especially at night and since aircraft radar systems cannot detect volcanic clouds. Satellite observations from the GOES satellite are useful currently for long range trajectory tracking and for measuring low level eruptions (Rose and Schneider, 1996), but upgrades of these satellites will lose valuable ash detection capabilities within a few years, and their observations are available only once every 30 minutes. The TOMS instrument, which can also detect and map volcanic clouds produces data over much of the globe from a polar orbiting satellite only once each day (Krueger et al 1995; Seftor et al, 1997).
Although designed to detect larger water and ice particles, ground-based meteorological radar systems have demonstrated valuable capability for eruption cloud monitoring and measurements (Harris et al, 1981; Harris and Rose, 1983; Rose et al, 1995). Dielectric characteristics of volcanic ash are markedly different from liquid water and ice, but they have recently been investigated (Adams et al, 1997). Continuously operated meteorological radar within 200 km of an active volcano can easily detect eruption clouds in all weather (Rose and Kostinski, 1994), and can accurately measure the height of eruption clouds, information that is vital for aircraft and for input into trajectory models (D' Amours 1994; Stunder and Hefftor, 1994) that can forecast the position of volcanic clouds after an eruption, based on winds aloft. A new generation of advanced meteorological radar systems (NEXRAD) have been installed in the US since 1992. These new radar systems have greatly improved the potential of ground-based systems to track volcanic clouds (Krohn, et al, 1994). In the case of Montserrat, the nearest NEXRAD system is in Puerto Rico, about 400 km WNW.
Installation of a NEXRAD-like ground based radar system at Antigua, about 30 km NE of Montserrat would provide 24 hour observations enabling notification and assessment of eruption intensity within a few minutes. The radar could track the movement of the volcanic cloud during its first few hours of movement and provide accurate altitude inputs for trajectory runs such as CANERM and VAFTAD. This capability would provide dedendable input into the initial eruptive events which would complement satellite data observations for longer range tracking. It would also be a very rich source of research data for volcanologists who wish to study eruption columns and ash cloud dynamics. The cost of a new generation radar system is substantial (~$1.3 million US) but low compared to an individual aircraft encounter. Given the risk that currently exists for Carribbean air traffic from Montserrat's activity, and the high probability of successful and timely mitigation this investment seems worth considering. After the eruption ends, the NEXRAD would be continually valuable for the measurements assessing the strength and position and trajectory of Atlantic hurricanes.
References Cited:
Adams, R., W. F. Perger, W. I. Rose and A. Kostinski, 1996, Measurements of the complex dielectric constant of volcanic ash from 4 to 19 GHz, J. Geophys. Res., 101: 8175-8185.
Casadevall, T J, editor, 1994, Volcanic Ash and Aviation Safety, U S Geol Surv Bull 2047.
D'Amours, 1994, Current and future capabilities in forecasting the trajectories , transport and dispersion of volcanic ash clouds in the Canadian Meteorological Centre, U. S. Geol. Surv. Bull 2047: Proceedings of International Symposium on Volcanic Ash and Aviation Safety, ed by T. Casadevall, pp 325-331.
Harris, D.M., W.I. Rose, R. Roe and M.R. Thompson, 1981, Radar observations of ash eruptions atMount St. Helens Volcano, Washington, U.S. Geol. Surv. Bull. 1250, 323-334.
Harris, D.M. and W.I. Rose, 1983, Estimating particle sizes, concentrations and total mass of ash in volcanic clouds using weather radar, J. Geophys. Res., 88, 10969-10983.
Krohn, M. D., L R Lemon and J Perry, 1994, WSR-88D Applications to volcanic ash detection, Proceedings of First Natioanl NEXRAD Users Conference, Norman OK, (October 1994).
Krueger, A.J., L.S. Walter, P.K. Bhartia, C.C. Schnetzler, N.A. Krotkov, I. Sprod, and G.J.S. Bluth (1995) Volcanic sulfur dioxide measurements from the Total Ozone Mapping Spectrometer (TOMS) instruments. Journal of Geophysical Research, 100, 14,057-14,076.
Rose, W.I., 1986, Interaction of aircraft and explosive eruption clouds: a volcanologist's perspective, AIAA Journal, 25: 52-58.
Rose, W. I. and A. B. Kostinski, 1994, Radar Remote Sensing of Volcanic Clouds, U. S. Geol. Surv. Bull 2047: Proceedings of International Symposium on Volcanic Ash and Aviation Safety, ed by T. Casadevall, pp 391-396.
Rose, W. I., A. B. Kostinski and L. Kelley, 1995, Real time C band radar observations of 1992 eruption clouds from Crater Peak/Spurr Volcano, Alaska, U. S. Geol. Surv. Bull. 2139 (Spurr Eruption, edited by T. Keith), 19-26.
Rose, W. I. and D. J. Schneider, 1996, Satellite images offer aircraft protection from volcanic ash clouds, EOS, 77: 529-532. (this paper also appeared in Earth in Space vol 9, no 6,, pp 9-11; 1997)
Seftor, C. J., N. C. Hsu, J. R. Herman, P. K. Bhartia, O. Torres, W. I. Rose, D. J. Schneider and N. Krotkov, 1997, Detection of volcanic ash clouds from Nimbus-7/TOMS, J. Geophys. Res., 102: 16749-16760 .
Stunder, B and J Hefftor, 1994, Modelling volcanic ash transport and dispersion, U. S. Geol. Surv. Bull 2047: Proceedings of International Symposium on Volcanic Ash and Aviation Safety, ed by T. Casadevall, pp 277-282.
Young, S, R S J Sparks, R Robertson, L Lynch and W Aspinall, 1997, Eruption of Soufriere Hills Volcano in Montserrat Continues, EOS, 78: 401-409.
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