Event Name : Pavlof 1975/9
|Start:||September 13, 1975 ||Observed|
|Stop:||March 1977 ||Observed|
|Lava flow: ||
|Lahar, debris-flow, or mudflow: ||
|Tephra plume: ||
|Duration: ||About 18 months, possibly longer ||
|MaxVEI: ||2 ||
|ColHeight: ||2400 m ||
Pavlof volcano was in eruption nearly continuously from September 13, 1975 until March, 1977. Jacob and Hauksson (1983) summarize the 1975-1976 activity as follows: "13 September - 06 October, 1975: Period of generally weak ash emissions, often likened to the chugging of a locomotive. Both harmonic tremor and explosion earthquakes recorded. Strong tremor recorded 13-15 and 23-24 September with increased activity. Possible lava flow observed in October. 09 September, 1976 - 04 December, 1976: Period of weak ash emissions including several episodes of stronger activity. Ash fall (light) at Sand Point on 09 September. Harmonic tremor recorded on 09 September, 18-22 October, and 10-22 November. Possible lava flow observed in December, may be spatter-fed or a lahar. Many explosions recorded, including some strong enough to be felt in Pavlof Bay (15-20 km)."
Shackleford (1977) summarizes the 1975 activity as follows: "Ash eruptions began from Pavlof on 13 September, 1975. There was no preceding rise in microearthquake frequency. Strongest activity took place in the months of September-October, ash columns achieving a height of 2400 m. A lava flow was reported moving down the N flank on 31 October, but similar observations in 1973 and 1974 were subsequently shown to be in error, so this report may be in error also. It may well be a lahar. Activity increased somewhat in December, with sporadic appearances of lava fountaining amidst the ash clouds. It was reported that 18:15 GMT 28 December saw a 30 sec. burst of lava from Pavlof that resembled a blow torch, was visible in broad daylight. From 03:55 to 04:10 GMT on 31 December a continuous series of lava pulses surged to heights of at least 150 m above the cone. One observer likened the activity of Pavlof to the chugging of a locomotive, rather than a steady state ash emission.
"Harmonic tremor has been recorded during eruptive periods, as well as explosion signatures. Some of the explosions have been strong enough to rock fishing boats 10-15 km away, in Pavlof Bay."
Matthew Sturm sent AVO an eyewitness account of the October 1975 lava flow, which he observed on October 7. His journal for that day reads: "During the night run the watch saw numerous red distress flares south of the ship and diverted to investigate. As they worked south, it became clear the flares were being sent up well inland on the Alaskan Peninsula, at which point it dawned on someone that perhaps it wasn’t flares at all. A little bit of trigonometry and it was soon clear that we were seeing Pavlof Volcano erupting. But just to be sure we stayed around and as the sun rose we could see a huge cloud above the 8200’ peak with red sparks embedded in the black cloud, while on the northern slopes below the summit we could make out black ash and lava spilling over the snow and glaciers on the upper reaches of the mountain. The volcano would be peaceful for a few minutes, then suddenly a cloud would jet up and billow out for three or four thousand feet above the mountain. The entire crew was mesmerized by the sight and we stayed there for over an hour watching."
Shackleford (1978) summarizes the 1976-1977 activity as follows: "Strombolian eruptions which began in September 1975 continued throughout 1976 and were continuing in 1977. In 1976 activity was at a somewhat lesser level than the preceding year. Possible lava flows reported in February and December." Please see Shackleford (1978) for a month-by-month description of activity.
Shackleford (1979) continues to summarize the activity in 1977: "Reports of the 1977 Pavlof activity are extremely sketchy and incomplete, in part due to very poor weather conditions. Since March 1977 there have been no reports of activity (which may well have continued beyond March) due to a lack of reporting personnel, rather than a lack of activity." Please see Shackleford (1979) for a month-by-month summary of 1977 activity.
McNutt (1999) calculates an eruptive volume of greater than 14.6 x10^6 cubic meters (dense rock equivalent) during the time period from September 13, 1975 through November 10, 1977.