Editing Mount Pinatubo (section)

===Modern Pinatubo===
* c. 79,000 BC:<ref>{{Cite journal|last1=Ku|first1=Yueh-Ping|last2=Chen|first2=Chang-Hwa|last3=Newhall|first3=Christopher G.|last4=Song|first4=Sheng-Rong|last5=Yang|first5=Tsanyao Frank|last6=Iizuka|first6=Yoshiyuki|last7=McGeehin|first7=John|date=February 1, 2008|title=Determining an age for the Inararo Tuff eruption of Mt. Pinatubo, based on correlation with a distal ash layer in core MD97-2142, South China Sea|url=http://ntur.lib.ntu.edu.tw/bitstream/246246/172549/1/18.pdf|journal=Quaternary International|series=Global Tephra Studies: John Westgate and Andrei Sarna-Wojcicki Commemorative Volume|language=en|volume=178|issue=1|pages=138–145|doi=10.1016/j.quaint.2007.02.025|bibcode=2008QuInt.178..138K |issn=1040-6182}}</ref> After a long period of [[dormant volcano|dormancy]], Modern Pinatubo was born in Ancestral Pinatubo's cataclysmic and most explosive eruptions, estimated to be five times larger than the June 1991 eruption. It deposited all around the volcano up to {{convert|25|km3|cumi|abbr=on}} of [[pyroclastic surge]] material up to {{convert|100|m|sp=us}} thick. The total volume of volcanic material ejected during the eruptions is unknown. The removal of so much material from the underlying [[magma chamber]] resulted in the Tayawan [[caldera]]. The violent eruptive period started by the eruption is referred to by Delfin as the ''Inararo Eruptive Period'', named after a village that was destroyed in the 1991 eruption.<ref name="Newhall"/>

Later eruptions of modern Pinatubo occurred episodically and lasted for periods much shorter than the repose intervals between them. Subsequent eruptions and eruptive period occurred about:
*c. 15,000 BC (Sacobia Eruptive Period)
*c. 7000 BC (Pasbul Eruptive Period). Its eruptions were as energetic, if not as voluminous as the Inararo eruptions. 
*c. 4000–3000 BC (Crow Valley Eruptive Period). This and the Mara-unot period's eruptions were smaller than the Inararo eruptions but about two to three times as big as that of 1991 based on the pyroclastic flow runout distances and depths of valley filling.
*c. 1900–300 BC (Maraunot Eruptive Period)
*c. AD 1500 (Buag Eruptive Period). Its eruptions were roughly the same size as those of 1991.

Each of these eruptions seems to have been very large, ejecting more than {{cvt|10|km3||}} of material and covering large parts of the surrounding areas with pyroclastic flow deposits. Some eruptive periods have lasted decades and perhaps as much as several centuries and might appear to include multiple large explosive eruptions.<ref name="Newhall"/>

The maximum size of eruptions in each eruptive period though has been getting smaller through the more than 35,000-year history of modern Pinatubo, but this might be an artifact of erosion and burial of older deposits. The oldest eruption of modern Pinatubo, Inararo, was also its largest.

The 1991 eruption was among the smallest documented in its geologic record.<ref name="Newhall"/>

The volcano has never grown very large between eruptions, because it produces mostly unwelded, easily erodible deposits and periodically destroys the viscous domes that fill its vents. After the Buag eruption (c. 1500 AD), the volcano lay dormant, its slopes becoming completely covered in dense [[rainforest]] and eroded into gullies and ravines. The c. 500-year repose though between the Buag and present eruptive periods is among the shorter repose periods recognized in its geologic history.<ref name="Newhall">{{cite book|editor-first1=Christopher G.|editor-last1=Newhall|editor-last2=Punongbayan|editor-first2=Raymundo S.|chapter=Eruptive history of Mount Pinatubo|chapter-url=http://pubs.usgs.gov/pinatubo/newhall/index.html|title=FIRE and MUD: Eruptions and Lahars of Mount Pinatubo, Philippines|url=http://vulcan.wr.usgs.gov/Volcanoes/Philippines/Pinatubo/Publications/FireMud/about_the_book.html|publisher=Philippine Institute of Volcanology and Seismology; University of Washington Press|year=1996|isbn=978-0-295-97585-6|access-date=October 5, 2008|archive-date=January 10, 2009|archive-url=https://web.archive.org/web/20090110162823/http://vulcan.wr.usgs.gov/Volcanoes/Philippines/Pinatubo/Publications/FireMud/about_the_book.html|url-status=live}}</ref>

====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]]

====Later eruptions====
[[File:Mount Pinatubo 20081229 01.jpg|thumb|[[Lake Pinatubo]], the crater lake resulting from the 1991 eruption, pictured here in 2008]]

Activity at the volcano remained low until July 1992 when a new lava dome started growing in the [[caldera]]. Volcanologists suspected that further violent eruptions could be possible, and some areas were evacuated. However, the eruption was only minor. The last eruption of Mount Pinatubo took place in 1993.<ref name="SI"/>

====Lake Pinatubo====
{{Main|Lake Pinatubo}}
[[File:Mount Pinatubo 6.jpg|thumb|An aerial view of Mt. Pinatubo and [[Lake Pinatubo]] in 2006]]
The 1991 caldera afterwards filled with water from annual monsoon rains and a [[Volcanic crater lake|crater lake]], [[Lake Pinatubo]], was formed. In 1992, a growing lava dome formed an island, which was eventually submerged by the lake. Initially, the lake was hot and highly [[acid]]ic, with a minimum [[pH]] of 2 and a temperature of about {{convert|40|C|F}}. Subsequent rainfall cooled and diluted the lake, lowering the temperature to {{convert|26|C|F}} and raising the pH to 5.5 by 2003.

The lake deepened by about {{convert|1|m|ft|sp=us}} per month on average, eventually submerging the lava dome, until September 2001, when fears that the walls of the crater might be unstable prompted the Philippine government to order a controlled draining of the lake. An estimated 9,000&nbsp;people were once again evacuated from surrounding areas in case a large [[flood]] was accidentally triggered. Workers cut a {{convert|5|m|sp=us|adj=on}} notch in the crater rim and drained about a quarter of the lake's volume.<ref>{{cite news|date=September 7, 2001|url=http://news.bbc.co.uk/2/hi/asia-pacific/1530182.stm|title=Filipinos return as volcano lake drains|publisher=BBC News|access-date=May 25, 2010|archive-date=April 21, 2021|archive-url=https://web.archive.org/web/20210421010958/http://news.bbc.co.uk/2/hi/asia-pacific/1530182.stm|url-status=live}}</ref>