Video Observations of Active Lahars and Other Volcanic Activity, Pinatubo Volcano, July-August 1992

Michael T Dolan (Geological Engineering, Michigan Technological University, Houghton MI 49931-1295; (906)487-2531; Fax (906)487-3371; Internet mtdolan@mtu.edu)

Because direct observations of active volcanic phenomena are still to scarce, the use of compact, high resolution video cameras in field work can provide useful documentation of active phenomena. The 1992 Summer at Pinatubo Volcano provided an opportunity to observe active lahars, secondary phreatic eruptions from cooling 1 year old pyroclastic flow deposits and lava dome extrusion in the summit crater. The video-poster presentation will present highlights of activity at Pinatubo during July and August of 1992 which could help researchers plan field work at this outdoor laboratory for various volcanic phenomena.

The eruption of Pinatubo Volcano 15 June, 1991 deposited thick pyroclalstic flows in the surrounding terrain. During the last year, rains have eroded material from the slopes generating lahars which fill low-lying valleys with often endanger villages, roads and bridges.

Deeply incised channels in the pyroclastic flow fans often were sources for mini-pyroclastic flows and small ash events. Also, meteoric water that percolates into the hot deposits (+300-500?C) generated enormous ash and pyroclastic flow producing explosions ranging from 7 to 24 km high.

On 5 July, 1992 an increase in background seismicity was recorded. Aerial surveys showed on 9 July a tuff cone generated by phreatic explosion formed in the middle of the crater lake. 14 July a lava dome pushed up through the center of the island. The dome grew quietly and by late August had reached a size of approx. 320m x 250m and 100m high.