Event Name : Pavlof 1996/9
|Start:||September 16, 1996 ||Observed|
|Stop:||January 3, 1997 ||Observed|
|Lava flow: ||
|Lahar, debris-flow, or mudflow: ||
|Tephra plume: ||
|Central eruption: ||
|MaxVEI: ||2 ||
|Eruption Product: || andesite ||
|Duration: ||About 2 and a half months ||
|ColHeight: ||9000 m ||
From Neal and McGimsey (1997): "Pavlof Volcano, historically the most active volcano in the Wrangell-Aleutian volcanic arc, began a vigorous strombolian eruption in mid-September, 1996 (Neal, 1996). The eruption, which continued into early 1997, occurred only two months after a 6-station seismic network was established near the volcano.
"A NWS observer in Cold Bay noted steam and incandescent ejecta above the volcano at about 0830 ADT on September 16. Analysis of seismic data and NOAA-12 and -14 AVHRR satellite images suggest that the eruption likely began at a very low level by September 11. Over the next few weeks, nearby residents observed intermittent strombolian eruptions from near the summit of the volcano. Pilots reported incandescent bombs the size of pick up trucks accompanied by minor ash clouds alternating with steam plumes rising from a few hundred meters to approximately 2 km above the volcano.
"Photographs from overflights on September 23 and AVO video from September 27-30 showed lava fountains emanating from two vents (figs. 4A and 4B). One vent was located on the east edge of an ~150-m diameter crater that indented the northwest summit of the volcano. A second, more active locus of fountaining was perched on the west edge of this crater 100-150 m below the summit. The two loci of fountaining were about 100 m apart and were generally not synchronous in activity. The east vent was less vigorous overall, producing intermittent puffs of gray to dark gray ash and steam tens of meters high. The west vent was the source of intermittent bursts of incandescent spatter up to 300 m high.
"By September 23, a small spatter cone was forming at the west vent and a collar of spatter, spatter-fed flows, and small lahars extended about 500 meters down the ~30 degree northwest flank below the summit crater. A lava flow formed by the coalescence and remobilization of heavy spatterfall and direct spill over from the west vent plunged down the steep flank, melting a narrow channel through seasonal snow and glacial ice. By September 29, the lava flow had reached the base of the cone, about 3.5 km from its source, and was beginning to widen into a lobate fan. Dark lahar deposits extended beyond the toe of this lava flow across the gently sloping ground northwest of the volcano, coming within about 40 m of AVO's seismic station PV6. By late October, a second lava flow issued from the east vent and on December 2, when videotaped by Alaska State Troopers, this flow was the more active of the two and had nearly reached the base of the cone in the saddle between Pavlof and Pavlof Sister.
"Eruptive activity became intermittent during the month of December. Seismicity decreased abruptly early on December 4 and ash was not visible above the regional cloud cover that obscured the summit of Pavlof for several days. Brief episodes of heightened seismicity occurred on December 10 (accompanied by at least one pilot report of ash) and December 27. The last reliable observation of ash emission occurred on January 3, although pilots and observers in Cold Bay reported possible minor ash in the steam plume over the volcano on a few occasions through February 6. Collapse of unstable agglutinate and hot fragmental debris on the steep upper cone may well account for some of these small ash plumes.
"During the first two weeks of the eruption, occasional elongate clouds (<50 km long) containing minor amounts of ash were detected on NOAA AVHRR satellite images (fig. 5). During the third week, both pilot reports and satellite image analysis documented larger but still diffuse ash clouds trailing as far as 175 km downwind, but they rarely reached more than ~6 km above the sea level. These clouds varied in length from a few tens to several hundred km and were observed intermittently, weather permitting, through late December. On November 4, accompanying some of the strongest seismicity of the eruption, a plume was visible in Bands 4-5 extending 350 km northeast of the volcano.
"In addition to elongate plumes, thermal anomalies associated with high temperature material were also recorded near the volcano's active vents and along the two main lava flow paths. The number of saturated pixels on AVHRR images varied from 1 - 15 indicating areas of up to about 18 km2 above 37 degrees C (A.L. Roach, oral communication, 1997). The last significant thermal anomaly was recorded in late December, however "warm" pixels were noted during daily analysis of AVHRR data into mid-February. Pilot reports and observations from Cold Bay confirm continued warm ground around the summit of the volcano as inferred from areas of snow-melt.
"As in the 1986 eruption, the 1996 activity produced rubbly, fragmental lava flows that extend in two main lobes down the northwest flank of the volcano (fig. 6). Early in the eruption, these flows occupied, at least in part, channels cut into the seasonal snow and glacial (?) ice on the volcano's flank. Melting of this snow and ice produced water and rock mixtures of unknown consistency that flowed out onto the more gently sloping terrain northwest (and possibly northeast) of the volcano. As of this writing, we do not know how far these lahars traveled or what impact they had on the Cathedral River and other drainages around Pavlof.
"Very light ashfall was reported in King Cove on the night of October 5-6, Sand Point on October 19, and Nelson Lagoon on October 28."
More from Neal and McGimsey (1997): "On October 3, based on observed plume heights, the FAA issued a Notice to Airmen (NOTAM) restricting flight below ~7 km and within 10 nautical miles of Pavlof. Higher levels of seismicity and more energetic ash plumes began on October 15 and in response, the FAA increased the altitude of restricted air space to approximately 8 km and the size of the restricted zone to a 25 mile radius around Pavlof. The FAA continued to enforce this restriction until January 27, 1997. Although Pavlof ash plumes reached altitudes of 30,000 feet or more on a few occasions, there were no serious disruptions in the North Pacific airways.
"There were, however, impacts on local air traffic. On November 4, a United States Coast Guard (USCG) C-130 operating at low level over the Bering Sea was struck by lightning. The flight crew also reported a "smoky" smell in the cockpit and a fine dust throughout the plane. Subsequent discussion with the USCG failed to positively identify the source of this material. However, based on NWS forecast winds during the time of this report, it appears unlikely that primary ejecta from Pavlof could have been the culprit; rather, it is possible that low level winds remobilized fine ash from the ground. No sample of the material was recovered for analysis.
"On November 27, 1996, a Reeve Aleutian Airways flight aborted landing into Sand Point when the pilot detected a brown haze that he interpreted to be ash from Pavlof."
McNutt (1999) calculates a dense rock equivalent volume of material erupted during this eruption as ~7 x10^6 cubic meters.