Geological Survey Circular 318 Eruption of Trident Volcano — Katmai National Monument, Alaska — February-June, 1953

The writer has estimated that 80-160 million cubic yards of lava and ash were extruded from the Trident vent by March 11, 1953. The volume of the volcanic pile during the writer's last observation on June 17, 1953, is estimated to have been 300-400 million cubic yards. The rate of emission was never constant, and actual ground measurements were not taken so that these estimates are to be regarded as orders of magnitude only.

The gases and finely comminuted ash of the fume cloud escaped from the joint openings over an area of 5-7 acres. The smoke column on February 18 rose over a mile into the air. With later observations in February and early March the height of this smoke column was always 1-2 miles in height, averaging perhaps 1-1/2 miles. Notable maxima were observed on March 9, March 24, and June 30. Before March 11 ??? the explosions forming the cloud occurred often enough (several to several dozen per minute) so that the column was always present. On March 11, however, the explosions were more sporadic, occurring 1-3 minutes apart, so that between bursts the smoke from the previous explosion would mostly drift away. From the later photographs moderate and, infrequently, explosive emission of steam with but little ash seems to have continued infrequently into June.

Before February 27, all observations of the eruption cloud indicated that it was moving southwest, northwest, west, or north before the prevailing winds. Observations of ash-covered ground as far away as the Bay of Islands, Naknek Lake are reported. Shortly before February 27 a snowstorm blanketed the entire Katmai National Monument area with clean snow. After this time all observations of the eruption cloud showed it to be drifting to the south, southeast, east, or northeast, and all fresh deposits of ash atop the new snow occurred in these areas within a 20-mile radius of the vent. Thus, although single observations made between February 15 and March 11 would seem to indicate a preferential deposition of the ash, actually the wind conditions had varied enough during this time to almost completely box the compass. It is very difficult to estimate the depth of the blanketing ash from a plane. Locally "drifts" of the ash from Trident Volcano, especially near the vent, may have been a foot to several feet in thickness. Probably within a radius of 15 miles of the vent an "average" thickness of the whole ash deposit would fall within the limits 0.01-0.1 foot. A cylinder of this radius and altitude would have a volume of 7 to 70 million cubic yards. Inasmuch as the area actually occupied by the ash is not flat but very mountainous these figures are probably conservative estimates.

A United Press release of February 26 reports that Charles L. Baker of the University of South Dakota analyzed samples of a dust deposit that covered portions of the State on February 19 and found them to be volcanic ash. He said, the article continues, that apparently the ash was the residue of recent volcanic eruptions in Alaska, carried there by strong winds. If this is true, the ash, if from the Trident vent, must have been derived from the initially violent explosions of February 15, 16, and (or) 17. These were the only eruption clouds which could have transported a very fine ash to a stratospheric wind zone. The aerial observations indicate that in this case, however, the amount of the ash transported beyond a 15-20 mile radius can be regarded as negligible from the view point of total volume determination.

The accompanying table gives the estimated maximum and average dimensions of the Trident lava flow at different dates. These estimates were derived by measuring plotted outlines and cross sections of the flow which were drawn to scale on a "blow-up" of the contour map of the area. Both the small scale of the original map and the estimated position of the flow borders render these figures approximations at best.

The volume of lava extruded as of March 11, 1953, has been computed as 70-90 million cubic yards. Together with the estimate of the amount of ash blown out this would make a total volume of 80-160 million cubic yards (or 0.015-0.029 cubic mile) as an order of magnitude. By June 17, 1953, it is estimated that the volume of the volcanic pile had risen to 300-400 million cubic yards (or 0.055-0.073 cubic mile). Note that these figures do not take the porosity of the deposits or the internal porosity of the actual rock fragments into account. It is believed that the error possible in the simple estimates makes further refinements pointless. For comparison the amount of ash and pumice which filled the Valley of Ten Thousand Smokes in the great eruption cf 1912 has been estimated to be about 1—1-1/2 cubic miles and the volume of the pyroclastic material derived from the entire Katmai eruption in 1912 has been estimated at 6-7 cubic miles (Griggs, p. 29, 31). From this comparison it is easily seen that Trident's eruption is but a small puff compared to those of the neighboring vents.

Table 1.—Estimated dimensions of lava flow from Trident Volcano, in feet