These thin, relatively fine-grained layers are lahar deposits produced by successive overflows of dikes along the Bambam River, about 35 km NE of Pinatubo volcano in the Phillipines. The photo was taken on October 13, 1991, a little more than a month after the end of the devastating 1991 eruption. Note the pen at the upper left for scale. By the end of 1991, rainfall-induced lahars had traveled 50 km down the Bambam River from the volcano.
A lahar, or volcanic mudflow, fills the banks of the Pasig-Potrero River on the east side of Pinatubo volcano in the Philippines on October 13, 1991. The lahar moved at a velocity of 3-5 m/sec, and carried a few meter-sized boulders. This lahar was not directly produced by an eruption, but was triggered by minor rainfall, which remobilized thick deposits of ash and pumice that blanketed the landscape. Devastating mudflows occurred at Pinatubo for years after the catastrophic 1991 eruption.
Lahars from Pinatubo volcano fill the broad Santo Tomás River valley SW of the volcano. Erosion along the south bank of the river has cut into the town of San Rafael. This photo was taken a month after the end of the 1991 eruption. Lahars produced by the redistribution of thick deposits of ashfall and pyroclastic flows caused extensive longterm economic devastation and were expected to continue for as long as a decade after the eruption.
Residents of the city of Bacolor, 38 km SE of Pinatubo volcano in the Philippines, perservere in the face of widespread devastation from lahars (volcanic mudflows). They are walking on the surface of a solidified 5-m-deep deposit of volcanic mud next to wires that are the original electrical power lines formerly high above the street level. Houses and businesses in the background of this September 1995 photo are buried to 2nd-floor levels. Rainfall-induced lahars were expected to redistribute ash and debris from the 1991 eruption for as long as a decade.
Owners of a service station in the city of Bacolor, 38 km SE of Pinatubo volcano in the Philippines, fight a losing battle with lahars. On September 12, 1991 (upper left), 10 days after the end of the 1991 eruption, they dig out gas pumps buried by 1-m thick lahar deposits. By November 30 (upper right) they had raised the pumps to the new ground level. Three years later, in September 1994, the pumps had again been raised, to a surface half the height of the garage opening. A year later, the station was abandoned, and a 5-m-high lahar deposit filled the garage. Photos by Chris Newhall (U.S. Geological Survey).
The seismogram for June 15, 1991, shows the heavy seismicity accompanying the catastrophic eruption of Mount Pinatubo in the Philippines. This seismic record shows earthquakes over a two-hour period beginning at 0508 hrs. The arrow points to the earthquake accompanying a major explosion at 0555 hrs, which was preceded by many large long-period earthquakes. At about 0640 hrs, continuous overlapping long-period earthquakes or tremor began, and much of the following record was saturated so that individual earthquakes could not be distinguished.
The climactic eruptions on June 15, 1991, created a 2.5-km-wide caldera at the summit of Pinatubo volcano. The elevation of the caldera floor is more than 900 m below that of the pre-eruption summit of Pinatubo. Steam rises from fumaroles on the caldera floor in this October 4, 1991, view from the north. The outer flanks of the caldera are stripped of vegetation and covered with deposits of airfall ash and pyroclastic surges.
Voluminous pyroclastic flows on June 15, 1991, from Mount Pinatubo in the Philippines, swept all sides of the volcano. The flat, light-colored areas in the foreground are pyroclastic-flow deposits that filled the Marella River valley on Pinatubo's SW flank to a depth of 200 m, more than the height of the Washington Monument. The dark hill at the center was completely surrounded by pyroclastic flows, which traveled 14 km down this valley.
Heavy ashfall from the June 15, 1991, eruption of Pinatubo volcano in the Philippines caused this World Airways DC-10 to set on its tail. About 4 cu km of ash was erupted on June 15. It accumulated to depths of 10-15 cm at this airfield at the Cubi Point Naval Air Station, 40 km SSW of Pinatubo.
The 1991 eruption of Pinatubo began on April 2 with a small phreatic eruption on the north flank. The eruptions occurred from a 1.5-km-long, E-W-trending fissure and produced several new explosion craters. Steam rises from a vent at the SW end of the fissure. Steam and minor ash were emitted after April 2, and increased prior to birth of a small lava dome at a NW-flank vent on June 7. Ash emission increased prior to the first large vertical explosion on June 12. During the climactic eruption on June 15 eruptive vents migrated to the summit..
Lahars produced devastating personal and economic disruption for many years after the 1991 eruption of Pinatubo in the Philippines. The towns of Barangay Manibaug Pasig, in the foreground of this February 26, 1994 view, and Mancatian in the distance were progressively buried over a several-year period. Construction of lahar levees provided only temporary protection from the massive downstream redistribution of ash and pumice from the 1991 eruption.
Floodwaters back up over the villages of Aglao and Dalanawan on the SW flank of Pinatubo volcano in the Philippines. Lake Mapanuepe was formed when lahars from the 1991 eruption of Pinatubo eruption traveled down the Marella River and dammed its tributary, the Mapanuepe River. Several villages were submerged by the rising lake waters. The level of the lake was stabilized in late 1992 at about this level by excavation of a trench through bedrock in the background. This prevented catastrophic rapid draining of the lake.