Misplaced Pages

#938061

68-403: A volcanologist is a geologist who studies the eruptive activity and formation of volcanoes and their current and historic eruptions. Volcanologists frequently visit volcanoes, especially active ones, to observe volcanic eruptions , collect eruptive products including tephra (such as ash or pumice ), rock and lava samples. One major focus of enquiry is the prediction of eruptions; there

136-412: A depiction of an erupting volcano, with a cluster of houses below shows a twin peaked volcano in eruption, with a town at its base (though archaeologists now question this interpretation). The volcano may be either Hasan Dağ , or its smaller neighbour, Melendiz Dağ. The classical world of Greece and the early Roman Empire explained volcanoes as sites of various gods. Greeks considered that Hephaestus ,

204-465: A key role in volcano explanations until the 16th century after Anaxagoras , in the fifth century BC, had proposed eruptions were caused by a great wind. Lucretius , a Roman philosopher, claimed Etna was completely hollow and the fires of the underground driven by a fierce wind circulating near sea level. Ovid believed that the flame was fed from "fatty foods" and eruptions stopped when the food ran out. Vitruvius contended that sulfur, alum and bitumen fed

272-420: A knowledge of its previous eruption in about 1500 AD. There is a local oral tradition suggestive of a folk memory of earlier large eruptions. An ancient legend tells of Bacobaco, a terrible spirit of the sea, who could metamorphose into a huge turtle and throw fire from his mouth. In the legend, when being chased by the spirit hunters, Bacobaco flees to the mountain and digs a great hole in its summit showering

340-815: A large area to be monitored easily. They can measure the spread of an ash plume, such as the one from Eyjafjallajökull 's 2010 eruption, as well as SO 2 emissions. InSAR and thermal imaging can monitor large, scarcely populated areas where it would be too expensive to maintain instruments on the ground. Other geophysical techniques (electrical, gravity and magnetic observations) include monitoring fluctuations and sudden change in resistivity, gravity anomalies or magnetic anomaly patterns that may indicate volcano-induced faulting and magma upwelling. Stratigraphic analyses includes analyzing tephra and lava deposits and dating these to give volcano eruption patterns, with estimated cycles of intense activity and size of eruptions. Compositional analysis has been very successful in

408-416: A quid pro quo manner, or bargaining approach which is sometimes used in prayerful interactions with saints, has been related (in the tradition of James Frazer ) to earlier pagan beliefs and practices. In 1660 the eruption of Vesuvius rained twinned pyroxene crystals and ash upon the nearby villages. The crystals resembled the crucifix and this was interpreted as the work of Saint Januarius . In Naples ,

476-502: A type of safety valve. The causes of these phenomena were discussed in the large number of theories of the Earth that were published in the hundred years after 1650. The authors of these theories were not themselves observers, but combined the observations of others with Newtonian, Cartesian, Biblical or animistic science to produce a variety of all-embracing systems. Volcanic eruptions and earthquakes were generally linked in these systems to

544-659: A university ( lecturer or professor ), running of laboratory experiments, data collection, and writing of scientific peer-reviewed papers for the scientific community to critique and advance knowledge and discovery. Volcanologists working for volcano observatories and museums work in close collaboration with academic researchers, but day-to-day tasks may also include the collection and curation of volcanic samples, writing of reports from monitoring stations, and public outreach relating to volcanic hazards and climate change Mount Pinatubo Events/Artifacts (north to south) Events/Artifacts Artifacts Mount Pinatubo

612-459: A weak explosion occurred on Mt. Pinatubo between 12:09 p.m. and 12:13 p.m., which produced a plume. The agency later confirmed it was a phreatic explosion produced by hydrothermal fluids near the surface, rather than a magmatic eruption. The word pinatubo could mean "fertile place where one can make crops grow", or could mean "made to grow", in Sambal and Tagalog , which may suggest

680-588: Is an active stratovolcano in the Zambales Mountains in Luzon in the Philippines . Located on the tripoint of Zambales , Tarlac and Pampanga provinces, most people were unaware of its eruptive history before the pre-eruption volcanic activity in early 1991. Dense forests , which supported a population of several thousand indigenous Aetas , heavily eroded and obscured Pinatubo. Pinatubo

748-736: Is currently no accurate way to do this, but predicting or forecasting eruptions, like predicting earthquakes, could save many lives. In 1841, the first volcanological observatory, the Vesuvius Observatory , was founded in the Kingdom of the Two Sicilies . Volcanology advances have required more than just structured observation, and the science relies upon the understanding and integration of knowledge in many fields including geology , tectonics , physics , chemistry and mathematics , with many advances only being able to occur after

SECTION 10

#1732782397939

816-820: Is known for its VEI -6 eruption on June 15, 1991 , the second-largest terrestrial eruption of the 20th century after the 1912 eruption of Novarupta in Alaska . The eruption coincided with Typhoon Yunya making landfall in the Philippines, which brought a dangerous mix of ash and rain to nearby towns and cities. Early predictions led to the evacuation of tens of thousands of people, saving many lives. The eruption severely damaged surrounding areas with pyroclastic surges , pyroclastic falls , and later, flooding lahars caused by rainwater re-mobilizing volcanic deposits. This destruction affected infrastructure and altered river systems for years. Minor dome -forming eruptions inside

884-505: Is of Etruscan origin, but unknown meaning. Volcanologists research many aspects of volcanic processes to better understand planetary formation or to monitor current and future volcanic eruptions in order to protect citizens living in volcanic hazard zones. Volcanologists work at universities, museums or other national research institutes (often including volcano observatories), or in industry. Volcanologists working in academia will be usually involved in teaching geology classes if based at

952-586: Is part of a chain of volcanoes which lie along the western side of the island of Luzon called the Zambales Mountains . Pinatubo belongs to the Cabusilan sub-range of the Zambales Mountains , which consists of Mount Cuadrado , Mount Negron , Mount Mataba and Mount Pinatubo. They are subduction volcanoes, formed by the Eurasian plate sliding under the Philippine Mobile Belt along

1020-652: The Hawaiian religion , Pele ( / ˈ p eɪ l eɪ / Pel-a; [ˈpɛlɛ] ) is the goddess of volcanoes and a popular figure in Hawaiian mythology . Pele was used for various scientific terms as for Pele's hair , Pele's tears , and Limu o Pele (Pele's seaweed). A volcano on the Jovian moon Io is also named Pele . Saint Agatha is patron saint of Catania , close to mount Etna, and an important highly venerated (till today) example of virgin martyrs of Christian antiquity. In 253 CE, one year after her violent death,

1088-614: The Manila Trench to the west. Mount Pinatubo and the other volcanoes on this volcanic belt arise due to magmatic occlusion from this subduction plate boundary. Pinatubo is flanked on the west by the Zambales Ophiolite Complex, which is an easterly-dipping section of Eocene oceanic crust uplifted during the late Oligocene . The Tarlac Formation north, east and southeast of Pinatubo consists of marine, nonmarine and volcanoclastic sediments formed in

1156-420: 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. The 1991 caldera afterwards filled with water from annual monsoon rains and a crater lake , Lake Pinatubo , was formed. In 1992, a growing lava dome formed an island, which was eventually submerged by

1224-541: The Buag and present eruptive periods is among the shorter repose periods recognized in its geologic history. 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 19 kilometres (62,000 ft) and which generated large pyroclastic surges extending up to four kilometres (2.5 mi) from

1292-542: The Pacific Ring of Fire and the Americas, usually invoking the forces of the supernatural or the divine to explain the violent outbursts of volcanoes. Taranaki and Tongariro , according to Māori mythology, were lovers who fell in love with Pihanga , and a spiteful jealous fight ensued. Some Māori will not to this day live on the direct line between Tongariro and Taranaki for fear of the dispute flaring up again. In

1360-640: The Philippines. The approved and declared net land area of 7,440.1 ha (18,385 acres) covers the barangays of Mawakat and Nabuklod in Floridablanca, Pampanga , plus a portion of San Marcelino, Zambales , and a portion of Barangay Batiawan in Subic, Zambales . On January 14, 2010, some 7,000 Aeta families from Zambales were officially granted the Certificate of Ancestral Domain Title (CADT) covering

1428-625: The United States. The U.S. Naval Base Subic Bay was 37 kilometers (23 mi) south of Pinatubo, and the extent of Clark Air Base was just 14 kilometers (8.7 mi) east of the volcano's summit. The volcano is near to about 6 million people. Even before the 1991 eruption, Mount Pinatubo had little topographic prominence : it was 1,745 m (5,725 ft) above sea level, only about 600 m (2,000 ft) above nearby plains , and only about 200 m (660 ft) higher than surrounding peaks, which largely obscured it from view. It

SECTION 20

#1732782397939

1496-569: The Zambales side of Pinatubo which includes the summit and Lake Pinatubo, officially becoming their lutan tua (ancestral land). The ancestral domain title covers 15,984 ha (39,500 acres) and includes the villages of Burgos, Villar, Moraza and Belbel in Botolan and portions of the towns of Cabangan , San Felipe and San Marcelino . Ancestral domain titles are awarded to a certain community or indigenous group who have occupied or possessed

1564-618: The abode of Apo Namalyari ("The lord of happenings/events"), the pagan deity of the Sambal , Aetas and Kapampangans living on the Zambales range. It was said to comprise the whole mountain range until Sinukuan of Mount Arayat (the god of the Kapampangans) became a strong rival of Namalyari. Their fight, which took place over the center plains, shattered the mountain into smaller bodies and Mount Arayat lost its center peak. Other versions have it that Pinatubo's peak shattered because of Namalyari's immense fury in an attempt to teach humans

1632-740: The advance had occurred in another field of science. For example, the study of radioactivity only commenced in 1896, and its application to the theory of plate tectonics and radiometric dating took about 50 years after this. Many other developments in fluid dynamics , experimental physics and chemistry, techniques of mathematical modelling , instrumentation and in other sciences have been applied to volcanology since 1841. Seismic observations are made using seismographs deployed near volcanic areas, watching out for increased seismicity during volcanic events, in particular looking for long period harmonic tremors, which signal magma movement through volcanic conduits. Surface deformation monitoring includes

1700-461: The caldera continued from 1992 to 1993. The 1991 eruption had worldwide effects. It released roughly 10  billion tonnes (1.1 × 10 short tons ) or 10 km (2.4 cu mi) of magma, bringing large amounts of minerals and toxic metals to the surface. It also released 20 million tonnes (22 million short tons) of SO 2 . It ejected more particulate into the stratosphere than any eruption since Krakatoa in 1883. In

1768-457: The caverns and sources of the heat were deep, and reached down towards the centre of the Earth, while other writers, notably Georges Buffon , believed they were relatively superficial, and that volcanic fires were seated well up within the volcanic cone itself. A number of writers, most notably Thomas Robinson, believed that the Earth was an animal, and that its internal heat, earthquakes and eruptions were all signs of life. This animistic philosophy

1836-671: The crater collapsed, slowly releasing approximately 160 million cubic meters (5.7 × 10 ^  cu ft) of water and sediment into the Maraunot River in Botolan, Zambales . On July 26, 2011, a 5.9 magnitude earthquake struck close to Pinatubo; however, no major damages or casualties were reported. On March 4, 2021, the PHIVOLCS raised alert level 1 over Mount Pinatubo after reporting an increase on its seismic activity. 1,722 volcanic earthquakes were also recorded within

1904-509: The deep fires. Observations by Pliny the Elder noted the presence of earthquakes preceded an eruption; he died in the eruption of Vesuvius in 79 CE while investigating it at Stabiae . His nephew, Pliny the Younger , gave detailed descriptions of the eruption in which his uncle died, attributing his death to the effects of toxic gases. Such eruptions have been named Plinian in honour of

1972-547: The eruption of Vesuvius in 1737 (1737, with editions in French and English). The Jesuit Athanasius Kircher (1602–1680) witnessed eruptions of Mount Etna and Stromboli, then visited the crater of Vesuvius and published his view of an Earth with a central fire connected to numerous others caused by the burning of sulfur, bitumen and coal. He published his view of this in Mundus Subterraneus with volcanoes acting as

2040-441: The existence of great open caverns under the Earth where inflammable vapours could accumulate until they were ignited. According to Thomas Burnet , much of the Earth itself was inflammable, with pitch, coal and brimstone all ready to burn. In William Whiston 's theory the presence of underground air was necessary if ignition were to take place, while John Woodward stressed that water was essential. Athanasius Kircher maintained that

2108-494: The flames his breath and the tremors his railing against the bars of his prison. Enceladus' brother Mimas was buried beneath Vesuvius by Hephaestus, and the blood of other defeated giants welled up in the Phlegrean Fields surrounding Vesuvius. The Greek philosopher Empedocles (c. 490-430 BCE) saw the world divided into four elemental forces, of Earth, Air, Fire and Water. Volcanoes, Empedocles maintained, were

Volcanology - Misplaced Pages Continue

2176-400: The following months, aerosols formed a global layer of sulfuric acid haze. Global temperatures dropped by about 0.5 °C (0.9 °F) in the years 1991–1993, and ozone depletion temporarily increased significantly. The volcano is about 87 kilometers (54 mi) northwest of Manila , the capital of the Philippines. Near Mount Pinatubo are former military bases that were maintained by

2244-512: The formation and eruptive activity of volcanoes . Volcanologists frequently visit volcanoes, sometimes active ones, to observe and monitor volcanic eruptions , collect eruptive products including tephra (such as ash or pumice ), rock and lava samples. One major focus of inquiry in recent times is the prediction of eruptions to alleviate the impact on surrounding populations and monitor natural hazards associated with volcanic activity. Geologists who research volcanic materials that make up

2312-464: The god of fire, sat below the volcano Etna , forging the weapons of Zeus . The Greek word used to describe volcanoes was etna , or hiera , after Heracles , the son of Zeus. The Roman poet Virgil , in interpreting the Greek mythos, held that the giant Enceladus was buried beneath Etna by the goddess Athena as punishment for rebellion against the gods; the mountain's rumblings were his tormented cries,

2380-415: The grouping of volcanoes by type, origin of magma, including matching of volcanoes to a mantle plume of a particular hotspot , mantle plume melting depths, the history of recycled subducted crust, matching of tephra deposits to each other and to volcanoes of origin, and the understanding the formation and evolution of magma reservoirs, an approach which has now been validated by real time sampling. Some of

2448-420: The lake. Initially, the lake was hot and highly acidic , with a minimum pH of 2 and a temperature of about 40 °C (104 °F). Subsequent rainfall cooled and diluted the lake, lowering the temperature to 26 °C (79 °F) and raising the pH to 5.5 by 2003. The lake deepened by about 1 meter (3.3 ft) per month on average, eventually submerging the lava dome, until September 2001, when fears that

2516-587: The land continuously in accordance with their customs and traditions since time immemorial. They have the legal right to collectively possess and to enjoy the land and its natural resources to the exclusion of others. Having the land title will protect them from others – including foreigners – exploiting their land without compensation to and consent from the indigenous tribes. In the past, the Aetas had to contend with mining companies, loggers, and recently, tourist companies who earn from Mount Pinatubo but do not compensate

2584-486: The late Miocene and Pliocene . The most recent study of Mount Pinatubo before the activities of 1991 was the overall geological study in 1983 and 1984 made by F. G. Delfin for the Philippine National Oil Company as part of the surface investigations of the area before exploratory drilling and well testing for geothermal energy sources in 1988 to 1990. He recognized two life histories of

2652-618: The local tribes. Long before Mount Pinatubo became famous for its cataclysmic eruption, Philippine president Ramon Magsaysay , a native of Zambales, named his C-47 presidential plane Mt. Pinatubo . The plane crashed into Mount Manunggal in Cebu province in 1957, killing the president and twenty-four others on board. The shape of Mount Pinatubo's caldera inspired New Clark City Athletics Stadium in Capas , Tarlac . The caldera formed and Lake Pinatubo has, since June 15, 1991, become

2720-468: The manifestation of Elemental Fire. Plato contended that channels of hot and cold waters flow in inexhaustible quantities through subterranean rivers. In the depths of the earth snakes a vast river of fire, the Pyriphlegethon , which feeds all the world's volcanoes. Aristotle considered underground fire as the result of "the...friction of the wind when it plunges into narrow passages." Wind played

2788-467: The meaning of fear and show how misdeeds will be punished. According to the native elders, Apo Namalyari induced the June 1991 eruption because of displeasure toward illegal loggers and Philippine National Oil Company executives who performed deep exploratory drilling and well testing on the volcano looking for geothermal heat from 1988 to 1990. Discouraging results from the wells forced the abandonment of

Volcanology - Misplaced Pages Continue

2856-477: The miniDOAS), which analyzes the presence of volcanic gases such as sulfur dioxide ; or by infra-red spectroscopy (FTIR). Increased gas emissions, and more particularly changes in gas compositions, may signal an impending volcanic eruption. Temperature changes are monitored using thermometers and observing changes in thermal properties of volcanic lakes and vents, which may indicate upcoming activity. Satellites are widely used to monitor volcanoes, as they allow

2924-423: The mountain, which he classified as "ancestral" and "modern" Pinatubo. Activity of Ancestral Pinatubo seems to have begun about 1.1 million years ago and probably ended tens of thousands of years or more before the birth of "modern" Pinatubo. Much of the rugged land around the present volcano consists of remnants of "ancestral" Pinatubo. It was an andesite and dacite stratovolcano whose eruptive activity

2992-404: The nature of volcanic phenomena. Italian natural philosophers living within reach of these volcanoes wrote long and learned books on the subject: Giovanni Alfonso Borelli 's account of the eruption of Mount Etna in 1669 became a standard source of information, as did Giulio Cesare Recupito's account of the 1631 eruption of Mount Vesuvius (1632 and later editions) and Francesco Serao 's account of

3060-479: The nearby peaks are the remnants of ancestral Pinatubo, left behind when the softer parts of the old mountain slopes were eroded by weathering . Ancestral Pinatubo is a somma volcano with modern Pinatubo as the new cone. Mount Dorst, to the east, is part of the dip slope of the ancestral Pinatubo. Several mountains near modern Pinatubo are old satellite vents of ancestral Pinatubo, forming volcanic plugs and lava domes. These satellite vents were probably active around

3128-516: The next initial onset time of an eruption, as it might also address the size of a future eruption, and evolution of an eruption once it has begun. Volcanology has an extensive history. The earliest known recording of a volcanic eruption may be on a wall painting dated to about 7,000 BCE found at the Neolithic site at Çatal Höyük in Anatolia , Turkey . This painting has been interpreted as

3196-525: 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. 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

3264-661: The prospect 13 months before the April 2, 1991, explosions. After being driven away by the 1991 eruption of Mount Pinatubo, in May 2009 some 454 Aeta families in Pampanga were given the first clean ancestral land ownership on Mount Pinatubo with the Certificate of Ancestral Domain Title (CADT) by the National Commission on Indigenous Peoples (NCIP), the government agency that deals with issues concerning indigenous people of

3332-437: The relics of St Januarius are paraded through town at every major eruption of Vesuvius. The register of these processions and the 1779 and 1794 diary of Father Antonio Piaggio allowed British diplomat and amateur naturalist Sir William Hamilton to provide a detailed chronology and description of Vesuvius' eruptions. Volcanologist A volcanologist , or volcano scientist , is a geologist who focuses on understanding

3400-664: The rise of molten rock to the surface. During the Renaissance, observers as Bernard Palissy , Conrad Gessner , and Johannes Kentmann (1518–1568) showed a deep intense interest in the nature, behavior, origin and history of the terrestrial globe. Many theories of volcanic action were framed during the late sixteenth mid-seventeenth centuries. Georgius Agricola argued the rays of the sun, as later proposed by Descartes had nothing to do with volcanoes. Agricola believed vapor under pressure caused eruptions of 'mointain oil' and basalt. Johannes Kepler considered volcanoes as conduits for

3468-537: The same time as the ancestral volcano and include the domes of Mount Negron, Mount Cuadrado, Mount Mataba and the Bituin and Tapungho plugs. 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: Each of these eruptions seems to have been very large, ejecting more than 10 km (2.4 cu mi) of material and covering large parts of

SECTION 50

#1732782397939

3536-588: The solid Earth are referred to as igneous petrologists. The word volcanologist (or vulcanologist ) is derived from the English volcanology ( volcano + -logy ), which was derived from the French volcanologie (or vulcanologie), which was further derived from the French word volcan (volcano), which was even further derived from Vulcanus , the Latin name of the Roman god of fire and metalworking . The Latin word

3604-476: The stilling of an eruption of Mt. Etna was attributed to her intercession. Catania was however nearly completely destroyed by the eruption of Mt. Etna in 1169, and over 15,000 of its inhabitants died. Nevertheless, the saint was invoked again for the 1669 Etna eruption and, for an outbreak that was endangering the town of Nicolosi in 1886. The way the saint is invoked and dealt with in Italian folk religion , in

3672-449: The summit in some river valleys . Fourteen hours later, a 15-minute blast hurled volcanic matter to heights of 24 km (15 mi). Friction in the up-rushing ash column generated abundant volcanic lightning . In March and April 1991, magma rising toward the surface from more than 32 km (20 mi) beneath Pinatubo triggered small volcano tectonic earthquakes and caused powerful steam explosions that blasted three craters on

3740-412: The surface and exploded in the reawakening volcano's first spectacular eruption. 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 5 km (1.2 cu mi) of material. The ash cloud from this climactic eruption rose 35 km (22 mi) into the atmosphere. At lower altitudes, the volcanic ash

3808-471: 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. 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,

3876-405: The surrounding land with rock, mud, dust and fire for three days; howling so loudly that the earth shakes. Aeta elders tell many stories about the history of the mountain, the best known being that it was once a Batung Mabye ( Kapampangan language for "living stone"). It was said to have been planted on a kingdom by a displeased sorcerer but relocated by a hero. The mountain was soon turned into

3944-557: The tears and excrement of the Earth, voiding bitumen, tar and sulfur. Descartes, pronouncing that God had created the Earth in an instant, declared he had done so in three layers; the fiery depths, a layer of water, and the air. Volcanoes, he said, were formed where the rays of the sun pierced the earth. The volcanoes of southern Italy attracted naturalists ever since the Renaissance led to the rediscovery of Classical descriptions of them by wtiters like Lucretius and Strabo . Vesuvius, Stromboli and Vulcano provided an opportunity to study

4012-459: The techniques mentioned above, combined with modelling, have proved useful and successful in the forecasting of some eruptions, such as the evacuation of the locality around Mount Pinatubo in 1991 that may have saved 20,000 lives. Short-term forecasts tend to use seismic or multiple monitoring data with long term forecasting involving the study of the previous history of local volcanism. However, volcanology forecasting does not just involve predicting

4080-423: The two authors. Thirteenth century Dominican scholar Restoro d'Arezzo devoted two entire chapters (11.6.4.6 and 11.6.4.7) of his seminal treatise La composizione del mondo colle sue cascioni to the origin of the endogenous energy of the Earth. Restoro maintained that the interior of the Earth was very hot and insisted, following Empedocles , that the Earth had a molten center and that volcanoes erupted through

4148-432: The use of geodetic techniques such as leveling, tilt, strain, angle and distance measurements through tiltmeters, total stations and EDMs. This also includes GNSS observations and InSAR. Surface deformation indicates magma upwelling: increased magma supply produces bulges in the volcanic center's surface. Gas emissions may be monitored with equipment including portable ultra-violet spectrometers (COSPEC, now superseded by

SECTION 60

#1732782397939

4216-444: The vicinity of the volcano since January 2021. On August 11, 2021, PHIVOLCS downgraded Mt. Pinatubo's Alert Level 1 to Level 0, due to "continued decrease in earthquake activity and a return to baseline seismic parameters". PHIVOLCS said it noted a "significant decrease" in volcanic earthquakes, with a total of 104 quakes or an average 2–3 events per day recorded from July 1 – August 1, 2021. On November 30, 2021, PHIVOLCS reported

4284-402: The volcano that the summit collapsed to form a 2.5 km (1.6 mi) wide caldera. 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. Activity at the volcano remained low until July 1992 when a new lava dome started growing in

4352-458: The walls of the crater might be unstable prompted the Philippine government to order a controlled draining of the lake. An estimated 9,000 people were once again evacuated from surrounding areas in case a large flood was accidentally triggered. Workers cut a 5-meter (16 ft) notch in the crater rim and drained about a quarter of the lake's volume. On July 10, 2002, the west wall of

4420-486: Was also its largest. The 1991 eruption was among the smallest documented in its geologic record. 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

4488-626: 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. Huge pyroclastic flows roared down the flanks of Mount Pinatubo, filling once-deep valleys with fresh volcanic deposits as much as 200 m (660 ft) thick. The eruption removed so much magma and rock from below

4556-512: Was much less explosive than modern Pinatubo. Its center was roughly where the current volcano is. The projected height of the mountain is up to 2,300 m (7,500 ft), or 1.43 miles above sea level if it were a lone peak, based on a profile fitting to the remaining lower slopes, or lower if it had more than one peak. The old volcano is exposed in the walls of an old 3.5 km × 4.5 km (2.2 mi × 2.8 mi) wide caldera , referred to as Tayawan Caldera by Delfin. Some of

4624-441: Was waning by the end of the seventeenth century, but traces continued well into the eighteenth. Science wrestled with the ideas of the combustion of pyrite with water, that rock was solidified bitumen, and with notions of rock being formed from water ( Neptunism ). Of the volcanoes then known, all were near the water, hence the action of the sea upon the land was used to explain volcanism . Tribal legends of volcanoes abound from

#938061