Johnston, D.M. 1997 The Impact of recent falls of volcanic ash on public utilities in two communities in the United States of America. Lower Hutt: Institute of Geological & Nuclear Sciences. Institute of Geological & Nuclear Sciences science report 97/05 iii, 19 p.
Abstract: This report describes visits to two United States communities affected by volcanic ash. The city of Anchorage in Alaska was covered by 3 mm of volcanic ash from the 1992 eruption of Mt Spurr. Yakima in Washington received 1O mm from the 198O Mt St Helens eruption. The purpose of the visits (Yakima in 1995 and Anchorage in 1996) were to gain information on the impacts of both eruptions by meeting with key utility providers and officials of the state government and the United States Geological Survey's Cascade and Alaskan volcano observatories (CVO and AVO). The impact of the 198O Mt St Helens and 1992 Mt Spurr eruptions highlight the vulnerability of urban areas receiving only a few millimetres of volcanic ash. In most cases thin ash falls cause disruption rather than destruction, mostly affecting transportation, electricity, sewage and stormwater systems. Most systems could be fully operational again within a few days. Water supplies are vulnerable during ash clean-up operations due to high demand. This highlights the need for a water management plan to handle excessive demands and should include procedures to fill reservoirs (if possible) on receipt of an ash fall warning and appropriate public information messages outlining water conservation measures There is also a need to retain a fire fighting water supply potential. Both communities (Yakima and Anchorage) were forced to undertake expensive and time-consuming clean-up operations. Vulnerable communities need to develop coordinated ash removal plans, that identify appropriate methods of ash removal, collection and disposal. The public needs to be adequately informed on what to do with volcanic ash. Falls of volcanic ash can disrupt electricity supply. Weather conditions during and after ash - fall will influence how ash adheres to insulating surfaces, with outages only occurring if the ash is wet (i.e. conductive). Low voltage systems are more vulnerable than higher voltage systems due to smaller weather sheds on insulators. Most outages are usually of short duration. The abrasive nature of ash can cause damage to mechanically moving parts, such as cooling fans. Immediate ash removal is the best mitigation option to prevent widespread outages. Following the ash falls, demand for information from the public caused overloads on the switch boards of many organisations in Yakima and Anchorage. This tied up a large number of staff and prevented them from attending to other essential tasks. The eruptions highlight the value of emergency management planning that identifies likely impacts on a specific community's lifelines and strengthens the links between agencies that will have to respond to such events. (auth)