Plate Tectonics

Convergent Boundaries occur where oceanic lithosphere is pushed back into the mantle, marked by oceanic trenchesand subduction zones. Two types are possible

When two plates of oceanic lithosphere converge, one of the oceaniclithosphere is subducted beneath oceanic lithosphere.

When ocean lithosphere runs into a plate with continental lithosphere, the oceanic lithosphere issubducted beneath the continental lithosphere.

Hotspot = an area in the Earth's mantle where hot material from the Earth's interior is moving upward

Hot spots

Hot spot in Hawaii

Types of Volcanoes

Diagram illustrating how calderas are formedCollapsed of the summitsummit subside

Structure of volcanoes

Many volcanoes contain a large depression

Craters= small depressions (i.e. less than 1 km across)= most craters result from the explosive activity by which the volcanic vent is cleared

Calderas= over 1 km across are called calderas= most calderas result from subsidence produced by the removal of large volumes of the underlying magma

Many present-day craters and calderas are filled with water, giving crater lakes.

Evolution of VolcanoesAn active volcanic landscape

Evolution of VolcanoesA volcanic landscape after a million years or so

Classes of Eruption

A. Effusive eruptions erupt mostly lava (generally basalt) and have little explosive activity.

B. Explosive eruptions are, well, explosive.

Volcanic Explosivity Index= logarithmic, each step is about 10 times larger than the previous step

IndexDescriptionPlume HeightVolume of EjectaClassificationExample0non-explosive< 100 m1000's m3Icelandic, HawaiianKilauea1gentle100-1000 m10,000's m3Hawaiian, StrombolianStromboli2explosive1-5 km1,000,000's m3Strombolian, VulcanianGaleras, 19923severe3-15 km10,000,000's m3VulcanianNevado Ruiz, 19854cataclysmic10-25 km100,000,000's m3Vulcanian, PlinianGalunggung, 19825paroxysmal>25 km1 km3PlinianSt. Helens, 19806colossal>25 km10's km3Plinian, Ultra-PlinianKrakatau, 18837super-colossal>25 km 100's km3Ultra-PlinianTambora, 18158mega-colossal>25 km 1,000's km3Ultra-PlinianYellowstone, 2 Ma

Some notes on the Explosivity Index

Proposed by Chris Newhall of the U.S. Geological Survey in 1982 as a means of quantifying the violence of eruptions.

Volume refers only to material ejected explosively; Hawaiian and Icelandic eruptions may erupt vast volumes of lava but eject very little material explosively.

The index isn't really concerned with material that falls immediately around the vent. Hawaii is noted for spectacular fire fountains and the total material ejected may be quite large, pushing the upper end of explosivity 1, but the material mostly falls back around the vent.

Effusive Eruptions

Icelandic Lava simply issues from fissures without building a volcano, though repeated activity may build shields. The greatest historic example was the Laki fissure flow of 1783, which killed about a fifth of the population of Iceland, mostly through crop and livestock destruction. Explosivity index 0. Note that merely being in Iceland doesn't make an Icelandic eruption; the Icelandic volcano Hekla has some of the largest explosive eruptions in history.

Hawaiian Basalt issues from long-lived central vents and builds shield volcanoes. Explosivity index 0-1.

Explosive Eruptions

Phreatic Steam explosions caused when lava or magma comes in contact with water. Large events may blast out craters called maars. The few explosive eruptions on Hawaii have been phreatic. One in 1790 killed several members of a Hawaiian war party passing close to Kilauea. Another series occurred at Kilauea in 1924 and one person was killed by flying ejecta. Explosivity index 0-1 in most cases but maar eruptions may go as high as 3 or so.

Strombolian Named for Stromboli, Italy, which has been popping mildly since Roman times and is nicknamed "lighthouse of the Mediterranean." Mild, long-lasting explosive activity confined to the immediate vent area. Typically associated with small stratovolcanoes (they don't erupt much material) and basalt or andesite lava. Explosivity index 1-2

Vulcanian Named for Vulcano, Italy, from which we also get the term volcano. Typical explosive eruption, with a large eruption cloud but not much pyroclastic flows. Generally associated with andesite stratovolcanoes. Explosivity index 2-4

Explosive Eruptions

Plinian Named for Pliny the Younger, who left a description of the eruption of Vesuvius in 79 A.D., and his uncle Pliny the Elder, who died in the eruption. Large eruption cloud, pyroclastic flows, and may collapse to create a caldera. Andesite or rhyolite stratovolcanoes. Mount Pelee, 1902 and Mount St. Helens, 1980 are examples. Explosivity index 4-6

Caldera-Forming (Ultra-Plinian) Catastrophic eruption usually associated with rhyolite stratovolcanoes or magma chamber collapse. Extremely large volume of pyroclastic flows that may travel for long distances. Tambora, 1815, Krakatoa, 1883, Katmai, 1912 and Mount Pinatubo, 1991 were historic examples. Mount Mazama 7000 years ago and Thera (Santorini) about 1500 B.C. are other famous cases. Explosivity index 6-8

Krakatoa volcano, Indonesia erupted violently in 1883 Prior to eruption, Krakatoa island group consisted of one large and two smaller volcanic islands lying around and within a prehistoric caldera 1883 eruption resulted in the removal of two of the three volcanic cones and the area between the three remaining remnant islands was filled by the sea to a depth of 250 m. eruptions began in May of 1883 with small explosions, large eruption (among the largest ever witnessed by people) occurred between 26 - 27 August and could be heard from a distance of 1000 km. Tsunamis over 40 m in height killed 36,000 people on the islands of Java and Sumatra. clouds of ash expelled were so dense that Jakarta (some 160 km away) was in total darkness by midday 27 August. Eruption cloud rose to a height of over 80 km and fell over an area of 800,000 km2. Large (i.e. over 0.5 m across) fragments fell over an area of 100 km2. About 20 km3 of ash erupted into the atmosphere, causing unusually cold weather for the next few years as the ash helped to black out the sun's rays.

Products of EruptionsLava Flows Pyroclastic Debris Bombs Lapilli Ash MudflowsLandslidesGases Steam Carbon Dioxide H2S SO2 HCl HF

Active Volcanoes in the Philippines (total 22 accdg Philvolcs)* dormant

Name of VolcanoLocationTypeElevation (m)base (m)Last eruptionBabuyan ClaroBabuyan Is.Stratovolcano8439201917TaalBatangas25-30 km caldera lake (500-100Tya)400xx1977Mt MayonAlbayStratovolcano2463xx2006Mt BulusanSorsogonStratovolcano1,56515,0002007Mt ParkerCotabatoStratovolcano1,82440,0001641Mt Banahaw*Quezoncomplex2,158XxunknownMt BiliranBiliran Is, Leytecomplex1,301xx1939Bud DajoJoloCinder cone6209,5001897CaguaCagayanstratovolcano1,1601,2001907Camiguin de BabuyanesBabuyan Isstratovolcano7123,2001857DidicasBabuyan IsDome volcano2281,2001990

* height 1,745m before eruption

Name of VolcanoLocationTypeElevation (m)base (km)Last eruptionMt Hibok HibokCamiguinstratovolcano1,3321,0001952Mt IrayaBatanesxx1,0095,5001454Mt IrigaCamarines Surstratovolcano1,14310,0001642Mt KanlaonNegros Is.stratovolcano2,43530,0002006MakaturingLanao del Surstratovolcano1,94029,0001882Mt MatutumSouth Cotabatostratovolcano2,28625,0001911Leonard KniaseffCompostela ValleyStrato in 203 caldera lake1,190xx120 ADMusuanBukidnonLava dome6463,0001867PinatuboTarlac,Pampanga, Zambalesstratovolcano1486*xx1991, 1993Smith volcano/Mt BabuyanBabuyan Is.Cinder cone, stratovolcano6884,5001924RagangLanao sur/Cotstratovolcano281532,0001916Mt ApoCot, Davaostratovolcano2,954unknown

Bukidnon, 4.5 km south of Valencia or 81 km southeast of Cagayan de Oro City (752'N, 12504.4' E)

Cotabato, approximately 30 aerial kilometers west of General Santos Cityand 44 kilometers south of Marbel (606.8' N, 12453.5' E)

Cotabato, 15 km north of Polomolok, South Cotabato and around 30 kmnorth-northwest of General Santos City (622'N, 12506.5'E)

PARKER (606.8' N, 12453.5' E)Approximately 30 aerial kilometers west of GSCand 44 kilometers south of Marbel

MUSUAN (752'N, 12504.4' E)Bukidnon, 4.5 km S of Valencia or 81 km SE of CDO

MATUTUM (622'N, 12506.5'E)Cotabato, 15 km N of Polomolok, 30 km N-NW og GSC

RAGANG (741.5 N, 12430.3 E)Boundaries of Lanao del Sur and Cotabato

MAKATURING (738.5N, 12420.5E) Lanao del Sur

LEONARD KNIASEFF (722.9'N, 1262.8' E)Compostela Valley

BABUYAN CLARO Babuyan Islands, Cagayan(1931.5'N, 121 57'E) PHYSICAL FEATURESElevation: 0.843 km Base Diameter: 0.920 m Type of Volcano: Stratovolcano

GEOLOGICAL FEATURESRock Type: Basalt Tectonic Setting: Babuyan (Bashi) Segment of Luzon-Taiwan Arc Age of Deposits: 2.32+/-0.35 Ma -- 1480+/-50 B.P (H.Bellon, J.C. Philippet, Brest. 1984)VOLCANIC ACTIVITYNumber of Historical Eruptions: 4Year: 1831, 1860, 1913, 1917Eruption Type: strombolian, phreatomagmaticVolcanic Hazards: lava flow, tsunamiwww.philvocs.dost.gov.ph

BANAHAW Boundaries of Laguna and Quezon provinces(1400N, 12129'E) PHYSICAL FEATURESElevation: 2.169 km Base Diameter: 25 km Type of Volcano: Stratovolcano, complexHotsprings: San Pablo-Tiaong hot/warm springs, Bakia warm/cold springs, Sampaloc warm springs, Mainit hot/warm springs and Cagsiay hot/warm springs Crater Lakes/Maars: Maars located south of Dolores: Lake Dagatan and Lake TicabAdjacent Volcanic Edifice: Mt. San Cristobal (1470 m asl, W), Mt. Banahaw de Lucban (1875 m asl, NE), Buho and Masalakot Domes (SW), Mt. MayaboboGEOLOGICAL FEATURESRock Type: Andesite Tectonic Setting: Macolod Corridor VOLCANIC ACTIVITYNumber of Historical Eruptions: 3Year: 1730, 1743, 1843Nature of eruption: explosiveVolcanic Hazards: debris avalanche, lahar and lake break-outwww.philvocs.dost.gov.ph

BUD DAJO Sulu, 8.05 aerial km SE of Jolo (5 59'N, 12113'E) PHYSICAL FEATURESElevation: 0.62 kmBase Diameter: 9.5 kmType of Volcano: Cinder ConeCrater Lakes/Caldera/Maars: Lake PanamaoAdjacent Volcanic Edifice: Matanding (400 m asl, NE) Guimba (482 m asl, E) and Sungal (518 m asl, SE)GEOLOGICAL FEATURESRock Type: BasaltTectonic Setting: Sulu Arc VOLCANIC ACTIVITYNumber of Historical Eruptions: 2Year: 1641 and 1897Eruption Type: phreatic (?)www.philvocs.dost.gov.ph

BULUSAN Sorsogon Province, 70 km southeast of Mayon Volcano and approximately 250 km SE of Manila (1246.2'N, 12403'E) PHYSICAL FEATURESElevation: 1.559 kmBase Diameter: 15 kmType of Volcano: Stratovolcano formed inside a calderaHotsprings: San Benon, Mapaso, San Vicente, MasacrotCraters and Fissure:1. Crater No. 1 or Blackbird Lake - 20 m in diameter and 15 m deep2. Crater No. 2 - roughly oval in shape, 60 m by 30 m and 15 m deep3. Crater No. 3 - approximately 90 m in diameter and 20 m deep4. Crater No. 4 - near the NE rim, opened during the 1981 eruptionFissure - located below Crater No. 4, measuring 5 to 8 m wide and about 100 m longAdjacent Volcanic Edifice: Mt. Homahan, Mt. Binitacan, Mt. Batuan, Mt. Calungalan, Mt. Calaunan, Mt. Tabon-Tabon, Mt. Juban and Mt. JormajanGEOLOGICAL FEATURESRock Type: Two-pyroxene andesite in Bulusan, dacite associated with calderaTectonic Setting: Bicol Volcanic ChainAge of Deposits: a) 1500300 years ( located at 1245'N, 12404'E)b) 5,480150 years ( located at Mapaso Stream Valley, 1245'N, 12404'E)c) 5,800100 years (located at a trail leading to Inlagadian, Casiguran, 1249'N, 12403'E)d) 33,5001,500 years (located at Magallanes Road, Juban, NW of Bulusan Volcano, 1249'N, 12358'E, sample taken from 30-40 m thick Irosin Caldera ashflow sheet)SOURCE: Newhall, C. and Cruz, J. (Unpublished data)VOLCANIC ACTIVITYNumber of Historical Eruptions: 16Latest Eruption/Activity: 21 March - 28 June 2006Eruption Type:1. Phreatic (e.g. 1918-1922, 1980)2. Strombolian (e.g. 1918-1919)3. Caldera-forming (e.g. 40,000 YBP)

CAGUA Cagayan, approximately 12 km south of Gonzaga and 14 km south ofPort Irene (1813.3'N, 1227.4'E) PHYSICAL FEATURESElevation: 1.16 kmBase Diameter: 12 kmType of Volcano: StratovolcanoHotsprings: Maasok Thermal Area(near the crater), Magrafil Thermal Area (NW), Manaring Thermal Area (5 km NNE) San Jose Thermal Areas (10 km NNE), Kabinlangan (3 km NW) and Paminta (2 km NNW)GEOLOGICAL FEATURESRock Type: Basalt, Andesite Tectonic Setting: Babuyan (Bashi) Segment of Taiwan-Luzon ArcVOLCANIC ACTIVITYNumber of Historical Eruptions: 2Year: 1860 and 1907

DIDICAS Babuyan Islands, Cagayan (19 04.6'N, 12212.1'E) PHYSICAL FEATURESElevation: 0.228 kmBase Diameter: 1.2 kmType of Volcano: Submarine/DomeGEOLOGICAL FEATURESRock Type: AndesiteTectonic Setting: Babuyan (Bashi) Segment of Luzon-Taiwan ArcVOLCANIC ACTIVITYNumber of Historical Eruptions: 6Year: 1773, 1856-1857, 1900, 1952, 1969, 1978 (Jan. 6-9, explosive, phreatic)Eruption Type: Submarine, phreatic, dome building

HIBOK-HIBOK Camiguin Island, located at the northwestern end of the Island (912.2'N, 12440.5E) PHYSICAL FEATURESElevation: 1.332 kmBase Diameter: 10 kmType of Volcano: Stratovolcano and dome complexHotsprings: Ardent Spring, Tangob, Bugong, Tagdo, Naasag, Kiyab Crater Lakes/Maars: CRATERS: Kanangkaan Crater (site of 1948 eruption) Itum Crater (site of 1949 eruption) Ilihan Crater (site of 1950 eruption)MAAR: Taguines Lagoon (located between Binone and Maac)Adjacent Volcanic Edifice: Mt. Vulcan ( 671 m high asl, NW of Hibok-Hibok ), Mt. Mambajao (center of Camiguin), Mt. Ginsiliban (581 m high asl, southernmost Camiguin), Mt. Uhay (N of Mount Ginsiliban); Domes and cones: Campana Hill, Minokol Hill, Tres Marias Hill, Mt. Carling, Mt. Tibane, Piyakong HillGEOLOGICAL FEATURESRock Type: Hornblende andesite and daciteTectonic Setting: Central Mindanao ArcVOLCANIC ACTIVITYNumber of Historical Eruptions: 5Latest Eruption/Activity: 1948 Sept. 31 - 1953 JulyEruption Type:1. Pelean (e.g. 1948-1952)2. Dome building with nuee ardente (e.g. 1871, 1949-1953)3. Solfataric activity with subterranean sounds ( e.g. 1897-1902)Eruption Sites during the 1948-1952 eruptions: Kanangkaan Crater (1948), Itum Crater (1949) and c) Ilihan Crater (1950).