Editing Mount Pinatubo (section)

====1991 eruption====
{{Main|1991 eruption of Mount Pinatubo}}
[[File:Pinatubo91eruption plume.jpg|thumb|right|The [[eruption column]] of Mount Pinatubo on June&nbsp;12, 1991, three days before the climactic eruption]]
[[File:Eruption of Mount Pinatubo, June 15, 1991.jpg|thumb|right|View to the west from Clark Air Base of the major eruption of Pinatubo on June 15, 1991. The June 15–16 climatic phase lasted more than fifteen hours, sent tephra about {{Convert|35|km|mi|abbr=on}} into the atmosphere, generated voluminous [[pyroclastic flow]]s, and left a caldera in the former summit region. Later dubbed Black Saturday, the day of darkness stretched for 36 hours.]]
A small blast at 03:41 PST on June 12 marked the beginning of a new, more violent phase of the eruption. A few hours later the same day, massive blasts lasting about half an hour generated big eruption columns, which quickly reached heights of over {{convert|19|km|ft}} and which generated large [[pyroclastic surge]]s extending up to {{convert|4|km|mi|spell=in}} from the summit in some river [[valley]]s. Fourteen hours later, a 15-minute blast hurled volcanic matter to heights of {{convert|24|km|mi|abbr=on}}. Friction in the up-rushing ash column generated abundant [[volcanic lightning]].

In March and April 1991, magma rising toward the surface from more than {{convert|32|km|mi|abbr=on}} beneath Pinatubo triggered small [[volcano tectonic earthquake]]s and caused powerful [[phreatic eruption|steam explosions]] that blasted three [[volcanic crater|craters]] on the north flank of the volcano. Thousands of small earthquakes occurred beneath Pinatubo through April, May and early June and many thousand of tons of noxious [[sulfur dioxide]] gas were also emitted by the volcano.<ref name="Pinatubo1991"/>

From June 7 to 12, the first magma reached the surface of Mount Pinatubo. Because it had lost most of the gas contained in it on the way to the surface, the magma oozed out to form a lava dome but did not cause an explosive eruption. However, on June 12, millions of cubic yards of gas-charged magma reached the surface and exploded in the reawakening volcano's first spectacular eruption.<ref name="Pinatubo1991"/>

When even more highly gas-charged magma reached Pinatubo's surface on June 15, the volcano exploded in a cataclysmic eruption that ejected more than {{Convert|5|km3|mi3|abbr=on}} of material. The [[eruption column|ash cloud]] from this climactic eruption rose {{Convert|35|km|mi|abbr=on}} into the atmosphere. At lower altitudes, the [[volcanic ash]] was blown in all directions by the intense cyclonic winds of a coincidentally occurring typhoon, and winds at higher altitudes blew the ash southwestward. A blanket of ash and larger [[pumice]] [[lapilli]] blanketed the countryside. Fine ash fell as far away as the [[Indian Ocean]] and satellites tracked the ash cloud several times around the globe.<ref name="Pinatubo1991"/>

Huge pyroclastic flows roared down the flanks of Mount Pinatubo, filling once-deep valleys with fresh volcanic deposits as much as {{Convert|200|m|ft|abbr=on}} thick. The eruption removed so much magma and rock from below the volcano that the summit collapsed to form a {{Convert|2.5|km|mi|abbr=on}} wide caldera.<ref name="Pinatubo1991"/>

Following the climactic eruption of June 15, 1991, activity at the volcano continued at a much lower level, with continuous ash eruptions lasting until August 1991 and episodic eruptions continuing for another month.

[[File:Tephra fall from 1991 eruption of Mt Pinatubo.gif|thumb|550px|center|The location of Mount Pinatubo and the regional ash fallout from the 1991 eruption]]