Mt St Helens 1980

Water Supply

After the 1980 eruption of Mt. St. Helens, some communities imposed an odds-even rationing system based on house numbers and dates and restricted water supply to the largest customers. One community imposed rationing only during the peak demand hours to ensure that line pressure was kept up in the event of a fire or some other high requirement situation. If uncontaminated ground water sources had not been available to most communities downwind of Mt. St. Helens, the demand would have exceeded supply to a much greater extent.

Increased water demand was experienced in many ash-affected communities (Blong 1984; Warrick et al., 1981). For example in Ellensburg, eastern Washington, demand during the first four days exceeded average demand 2.5 times (Warrick et al., 1981).


The 8-hour explosive eruption of Mt. St. Helens in Washington State on 18 May 1980 spread volcanic ash over central Washington and a large part of the Western United States. Yakima, 140 kilometers east of the volcano, received about 10 mm (0.4 in) of volcanic ash from the eruption. By the next day about 15 times the usual amount of solid matter was being removed from the pre-treatment processes at Yakima's sewage-treatment facility. Ash was also observed in the raw sludge in the primary clarifiers. Two days later, it was evident that the facility was suffering as vibrations were occurring in the grit classifier and the gearbox of the mechanically cleaned bar screen. Raw sludge lines became plugged and pumping difficulties were experienced. On May 21, equipment failures and shutdowns occurred, and city officials issued the following press release (Blong, 1984):

Press Release

Office of City Manager, City of Yakima, May 21, 1980

City Manager's Office announced this morning a decision to bypass the Yakima Wastewater Treatment Plant with sewage flow to the Yakima River, due to the disaster conditions from the volcanic ash. This decision was arrived at through consultation with the Washington State Department of Ecology.

We anticipate the bypass to be effective May 22, 1980, and to last indefinitely.

The specific reasons for the bypass are as follows:

  • Volcanic ash and grit accumulations in the system form unpumpable masses forcing equipment and operational failures.
  • Trickling Filter rock media is stripped by grit which destroys its ability to remove pollutants.
  • Abrasive wear on equipment may put the plant out of operation indefinitely and also cause damage to a major investment in new equipment installed as part of the current plant upgrading.

The conditions of the bypass include the following:

  • Regular testing of influent to determine when the grit content is low enough to handle in the plant.
  • Lines and equipment will be cleaned and readied for service.
  • We will assess equipment damage and take any available measures to prevent additional damage.
  • We will monitor river conditions which at this time are most favorable with high flows.
  • We will provide full documentation of problems, discussions, tests, remedial efforts and other actions.

The total damage to the Yakima plant was estimated at US$4 million, and primary treatment of sewage resumed on May 25.

Lessons from Yakima. This experience led public works officials to compile a list of things to do in order to protect waster water disposal equipment and help other cities that might experience similar ashfall (Blong, 1984):

  1. Cover all external equipment with plastic.
  2. Shut down all equipment not absolutely required.
  3. Shut down ventilation equipment where possible.
  4. Place all pre-treatment equipment into operation and adjust for maximum removal rates.
  5. Place all primary clarifiers into operation and increase pumping rates.
  6. Pump all grit and ash into one digester until conditions improve, then dump the contents.
  7. Shut down the biofilters and cover with plastic.
  8. Monitor all processes for introduction of grit and ash.
  9. Monitor torque or current on all motor driven devices.
  10. Grease everything subject to a dusty atmosphere, and those subject to pumping gritty material.
  11. Filter or change out gear lube weekly; flush with solvent recommended by the manufacturer.
  12. Alert the public to the consequences should they introduce this material into the sewer system.
  13. Notify regulatory agencies and public health officials.
  14. Formulate a plan to bring the plant processes and equipment back on line.
  15. Contact equipment manufacturers for their assistance.
  16. Step up preventive maintenance scheduling until the system is completely purged of contaminants.


The transportation network was impacted from ashfall. Roads were closed for up to two weeks in the worst hit regions due to visibility and traction issues for vehicles. 185 miles (298 km) of roads and highways and 15 miles (24 km) of railway were destroyed or extensively damaged (USGS, 1997).

There were lots of reported cases of ash damage to engines and motors clogging, resulting in overheating and damage. Pycroclastic flows and lahars deposited up to 2 m (6.5 ft) of debris onto roads near valleys down from Mt. St. Helens. In total 300 km (187 miles) of road and 48 road bridges were destroyed or extensively damaged (Blong, 1984).

Many vehicles had to be written off due to ash infiltration. One vehicle had 450 lbs (204 kg) of ash inside the vehicle. 165 of the State Patrol fleet in eastern Washington were incapacitated from ash cover, of those 50 were written off due to damage (Blong, 1984).

Air travel was severely affected by the eruption with some airports in eastern Washington closed up to 2 weeks due to poor visibility and runway conditions. Thousands of flights were cancelled due to this and further delays.

Power network

Fine-grained ash shorted electrical circuits and brought down electrical transformers. Most of these outages were short in durations occurring a few days after the eruption. A subsequent eruption a week later was accompanied by rainfall (Wilson et al., 2009). Low voltages lines and substations experienced numerous outages due to insulator flashover where thicknesses exceeded 5 mm (0.2 in) when wet. These insulator flashovers resulted in a number of reported cases of wooden electricity poles catching fire.

The Bonneville Power Administration (BPA), which transmits electricity across much of the Pacific Northwest, experienced 25 momentary and 25 sustained outages in the initial 10 days following the eruption (Blong, 1984).

The ash had a greater conductivity with a decrease in grain size. This triggered a trend of increased flashovers with distance from the volcano (Wilson et al., 2009).

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