ICAO - 9691
Manual on Volcanic Ash, Radioactive Material and Toxic Chemical Clouds
|Publication Date:||1 January 2015|
INTRODUCTION TO PART I
Humanity has a primeval fear of volcanic eruptions as a manifestation of the awesome and capricious power of nature, totally beyond our control and more often than not the deliverer of death and destruction. Although there are hundreds of active volcanoes around the world, they are not evenly distributed, but generally located together in well-known geologically active regions.
The highest concentration of active volcanoes lies around the rim of the Pacific Ocean, the so-called "ring of fire", which stretches northwards, more or less continuously, along the western edge of South and North America, across the Aleutian and Kurile Island chains, down through Kamchatka, Japan and the Philippines and across Indonesia, Papua New Guinea and New Zealand to the islands of the South Pacific. Other active regions are to be found in Iceland, along the Great Rift Valley in Central and East Africa, and in countries around the Mediterranean. This distribution is shown on the map provided as the frontispiece.
The behaviour of erupting volcanoes ranges from the quiet, steady effusion of lava at one extreme to highly explosive eruptions at the other which blast several cubic kilometres of glass particles and pulverized rock (volcanic ash) and corrosive gases high into the atmosphere and over a wide area for several days. Most people are familiar with the quiet activity typical of the volcanoes in Hawaii, where one can even touch the edge of the slowly moving lava flow; this is not the type of volcano that is of concern to aviation.
Aviation is only concerned with the explosive type of eruption,
which presents a direct threat to aircraft in flight and major
operational difficulties to aerodromes located downwind of the
resulting ash cloud. The provision of warnings to aircraft in
flight and aerodromes downwind of volcanic eruptions and volcanic
ash clouds necessitates close operational coordination between the
international aviation community, aviation meteorologists and
vulcanologists. Coordination between the aviation community and
meteorologists is of long standing, going back to the beginning of
aviation, and is based upon well-established international
arrangements and procedures; but coordination with the various
Vulcanological observatories are the first line of defence. They are usually sited in strategic locations from which one or more active volcanoes may be monitored. The wealth of continuous data from the various sensors sited on and around the volcanoes has to be analysed and interpreted by vulcanologists. If an explosive eruption is observed or if the analysis of the monitoring data indicates that such an eruption is imminent, this information has to be sent quickly through pre-arranged channels of communication to an agreed list of recipients, including the civil aviation and meteorological authorities, and then to pilots of aircraft which could be affected.
This is the basis of the ICAO International Airways Volcano Watch (IAVW). Unfortunately, and for obvious reasons, not all active volcanoes around the world are monitored. Moreover, explosive eruptions have a tendency to occur with little or no warning from volcanoes which have not erupted for hundreds of years. It was clear from the beginning that a dedicated volcano observing network could not be established specifically for aviation; the cost alone would have been prohibitive. In order to expand the volcano observing sources, therefore, recourse was made to other organized international networks of observatories such as meteorological, climatological and hydrological stations and to national organizations which maintain disciplined personnel in remote mountain areas in which volcanoes may be located, such as forestry, police, military, customs/immigration posts, and also disaster relief agencies. In all cases, unstinted cooperation was offered to ICAO by States and international organizations in the establishment of the IAVW, and in this way coverage was extended by making maximum use of existing resources. Pilots themselves are also an important source of information on volcanic activity and volcanic ash cloud, and in this regard ICAO has developed a format for a special air-report of volcanic activity which pilots are encouraged to use when reporting volcanic activity to air traffic services units.
Finally, considerable progress has been made in the detection of volcanic ash from meteorological satellite data, especially data in certain of the infrared wavelengths, and the forecasting of volcanic ash cloud trajectories using computer models. The techniques and equipment needed to accomplish this work are not available in all meteorological watch offices (MWOs). ICAO, therefore, has designated, based upon advice from the World Meteorological Organization (WMO), certain specialized meteorological centres having the necessary capability to serve as volcanic ash advisory centres (VAACs). These centres provide advice to MWOs and area control centres (ACCs) in their area of responsibility of the forecast trajectory of the volcanic ash and the flight levels likely to be affected. The MWO and ACC then issue the required SIGMET and notice to airmen (NOTAM) messages, respectively, to pilots, based on the advice received.
The view is prevalent in the aviation community, rightly or wrongly, that there must have been an increase in explosive volcanic eruptions during the past twenty years or so. Otherwise, how to explain the apparent sudden appearance of volcanic ash on the scene as a serious hazard to aircraft operations? This view gives rise to some amusement among vulcanologists, who are more accustomed to consider volcanic eruptions over periods of thousands of years.
Any attempt to discern trends in volcanic eruptions from the historic record is fraught with difficulties. That there has been an overall increase in volcanic eruptions reported over the past two hundred years is evident, but this trend has closely paralleled the increase in the global population and its spread to all corners of the world over the same period. That this upward trend in volcanic eruptions is almost certainly due to more effective communications and increased reporting is illustrated by the sudden and temporary decrease in reports of volcanic eruptions during the two World War periods and during the Depression of the 1930s, when global communications were dislocated. Similarly, temporary increases in reports of volcanic eruptions around the world follow closely on the heels of a major volcanic eruption, no doubt due to the wide publicity accorded the event.
It would not, therefore, be surprising if the apparent "recent" increase in volcanic eruptions, cited by some observers as the likely cause of volcanic ash emerging as a hazard to aviation, were to become self-fulfilling due to the increased vigilance and reporting introduced by the IAVW.
Another factor to be considered is the steady increase in aircraft operations during the past twenty years, especially around the Pacific rim, most of which have involved aircraft powered by jet turbine engines, and especially the high bypass ratio engines, which are inherently more susceptible to volcanic ash than piston-engined aircraft.
Wherever the truth of the matter lies, the last twenty years have certainly seen the emergence of volcanic ash as a serious hazard and financial cost to aircraft and aerodrome operations. With the cooperation of States through their civil aviation, meteorological, pilot and vulcanological communities and with the assistance of international organizations concerned, the IAVW has been developed to respond to this threat.