Mount Pinatubo is located in the southern part of Luzon. Luzon is an island in the Philippines situated approximately northwest of the capital city Manila. Mount (Mt) Pinatubo is one of the biggest volcanoes in the Philippines. For approximately 5 centuries, that mountain has been dormant, but in the mid 1991 Philippines as well as the whole world was awaken to one of the major geological events considering the volcanic eruption of the mountain. According to Rosenberge (2008), Mount Pinatubo experienced a powerful eruption in June 15 1991 ejecting large amount of ash and gas into the atmosphere leading to a huge cloud of volcanic ash that rose as high as 22 miles and spreads more than 300 miles away. The eruption became one of the major humanitarian disasters ever witnessed in Philippines attributed to natural disasters taking into consideration the loss of several lives as well as destruction of massive amount of property both public and private. For instance, it is estimated that at least 800 lives were lost, more than 1 million people displaced with more than half a billion damage in economic and property spheres. 

Geological setting of Mount (Mt) Pinatubo

The Zambales Ophiolite Complex edges Pinatubo on the west. It is an easterly-dipping section of Eocene ocean crust uplifted during the late Oligocene. It is noteworthy that the Tarlac Formation composed of marine, volcaniclastic and non-marine sediments on the three crucial ends of the Mountain that is the east, north, and south east. Studies indicate that the Tarlac Formation of Pinattubo took place in the late Miocene and Pliocene. Mt Pinatubo is part of a chain of combined volcanoes situated along the Luzon arc. The arc of the volcanoes is believed to be the result of the subduction of the manila trench to the west. 

Geology of the event

The 15 June 1991 event on Mount (Mt) Pinatubo was a volcanic eruption. This volcanic eruption is considered one of the biggest eruptions in the 20th century second to the 1912 eruption of Katmai-Novarupta (Alaska). According to Riikonen (2001), the violent volcanic eruption of Mt Pinatubo ejected several billion cubic meters of high-speed gas, hot ash, mudflows, and pyroclastic debris into the atmosphere, which later settled on the adjacent land. The voluminous volcanic ashes ejected from the fiery bowel of the eruption that went as high as 300 miles covered the atmosphere-turning day into night over Luzon area (Guzman, 2004). The volcanic eruption emitted approximately 15 million tons of sulfur dioxide into the atmosphere, which reacted with water for a hazy layer of particles consisting primarily of sulfuric acid droplet (Rosenberge, 2008). As a result of eruption a coincidental typhoon took place causing a major shower in the Luzon area leading to massive mudflow and debris from the mountain to the adjoining lowlands.  

Precursor activities

A massive earthquake of the July 1990 preceded the events of the Mt Pinatubo eruption in the mid 1991. This earthquake, which took place approximately 100 km northeast of Pinatubo region, measured magnitude 7.8 on the Richter scale. It is believed that the earthquake reawakened the mountain, which was dormant for almost 500 years since its last eruption. Despite the fact that the mountain appeared to be still on slumber even after the earthquake, geological studies indicate that it squeezed and shook the Earth’s crust underneath the volcano causing landslide, subsequent minor local earthquakes, and an increase in steam discharge from an already existing geothermal region. This claim can be justified by the fact that a few months after the major 1990 earthquake, small earthquakes resulting from the magma forcing its way beneath Mt Pinatubo were felt by the villagers. Additionally, a powerful steam ruptured three craters on the north edge of the volcano. It is noteworthy that locals of Luzon region continued to experience a series of small earthquakes and tremors throughout April to early June. It was a clear justification that Mt Pinatubo was reawakening and it was a matter of time before it erupted. The series of earthquakes around the area felt by the villagers prompted volcanologists to begin studying the mountain’s possible future eruption.

Impacts of Mount Pinatubo’s eruption on local communities

The 1991 Mt Pinatubo’s eruption is one of the most severe natural disasters that Philippines has ever witnessed in the past considering its impact on lives of the locals, property, natural resource, infrastructure, and economy. In other words, the disaster caused by eruption of Mt Pinatubo was particularly devastating for the locals (Park, 2001). The impact of the Mt Pinatubo’s eruption on the society, environment, and the economy ranged from mild to severe depending on the distance of the affected area from the active volcano. 

Physical impact

Physical impacts of the 1991 Mt Pinatubo’s eruption includes all the immediate effects that results from the eruption itself. Key among the primary impact of Mt Pinatubo eruption include ejection of ash and dust into the stratosphere, lava flow, pyroclastic debris and dangerous gases such as sulfur dioxide. During explosive eruption of Mt Pinatubo, large amount of larva was expelled from fiery bowl of the mountain. Large amount of hot ash and dust was ejected into the air and raised high reaching an altitude of more than 30 kilometers and spreading more than 300 miles. Additionally, more than 15 million tons of sulfur dioxide was expelled into the stratosphere during the fierce eruption on Mt. Pinatubo.  Volcanic bombs consisting majorly of pyroclastic debris were thrown from the eruption. 

Secondary impact

The secondary impact of Mt Pinatubo consists of the after-eruption effects. Secondary impacts of volcanic eruption evolve from the primary impact. Secondary effects of Mt. Pinatubo eruption can be classified into three major categories namely the physical, social and economic impacts. Notable physical impact of Mt Pinatubo includes the expulsion of dust and ash into the sky, which blurred the vision turning day into night in the Luzon region.

The local as well as nearby province farmlands, towns, and villages were covered with a heavy sheath of dust and ash, which emanated from the eruption making most of the places dusty and slippery. During the volcanic eruption of Mt Pinatubo, tropical storm (typhoon) was passing causing a heavy downpour in the region. The ashes and dust from the volcano and water from rain mixed up creating a lahar, which descended on the low lands damaging natural resources. For instance, approximately 18,000 hectares of forest were damaged causing immense clogging of several major river systems namely the Santo Tomas, Balin-Baquero Bacao, Pasig-Potrero, Gumain, Bamban, Porac, Tarlac, and Abacan Rivers. Additionally, the mixture of sulfur dioxide and rainwater contaminated water supplies as it generated sulfuric acid. 

Notable economic effects of Mt Pinatubo eruption include damages to the infrastructure, factories, complete ruin of Clarke airbase, damage to farm lands and animals. Rosenberge (2008) asserts that the estimated economic damages as result of the volcanic eruption stood at approximately one-half of a billion dollars. Guzman (2004) explains that key infrastructure that was damaged includes roads, bridges, communication network, irrigation and flood control systems, school buildings as well as manufacturing plants. Most of these infrastructures were damaged by the flow of lahar. Agriculture is an important industry in the Philippines economy, thus, it was imperative to consider it when analyzing economic effects of Mt Pinatubo eruption. For instance, heavy dust and ashes from the volcano covered large tracks of commercial farmlands and lahar damaged various irrigation systems, killed animals, and destroyed landscape altering land use in various provinces, particularly Zambales, Tarlac and Pampanga. In other words, agricultural property worth several million dollars were damaged ranging from crops and fishery to livestock in the aftermath of the Mt Pinatubo eruption devastating several families which was dependant on agricultural production. 

Social effects of Mt Pinatubo eruption were more disheartening to the locals and nearby provinces considering the immense impact on lives, alteration of social life, and destruction of property. More than 800 lives were lost, over 200 people were injured and at least 23 missing. It was one of the major humanitarian crises in Philippines. Flowing lahar and weight of ashes has been pinpointed to the major cause of several casualties during the event. Several houses and personal property were partially or totally destroyed during the event leaving people homeless. It is estimated that approximately 1 million people were displaced from their homes to evacuation centers. It is unfortunate that a score of lives were lost owing to various diseases especially in the evacuation centers. Key among the killer diseases were acute respiratory infections (ARI), measles and diarrhea. The locals were also faced by threat of hunger and poor sanitation taking into consideration they were heavily depending on relief especially food,  clothing, clean drinking water, clothing and shelter. 

1991 Pinatubo eruption in comparison to the 1980 Mt. St. Helens

The Pinatubo eruption of mid 1991 was the largest in terms of size and potential effect compared to the 1980 Mt. St. Helens considering the fact that ashes expulsion into the air during the Mt. St. Helens eruption went as high as 16 miles when Pinatubo’s eruption reached an altitude of 22 miles. Additionally, many scholars consider the Pinatubo eruption as the second biggest volcanic eruption in the 20th century in terms of its magnitude and effect. It is noteworthy that Mt. St. Helens eruption was not devastating in terms of humanitarian crisis and destruction of property compared to Pinatubo eruption owing to the fact that the area was surrounded by large forest with less human settlement unlike in Philippines where the eruption took place in densely populated area. Despite the fact that the pyroclastic flows of Mt. St. Helens eruption was moving at a speed of up to 670 miles per hour, it does not mean that the eruption had a serious potential effect in the surrounding. Mt Pinatubo pyroclastic flows were propelled by the raging waters of the tropical storm that hit the region; otherwise the magma could be flowing at a very slow pace. 

Reducing impacts of the 1991 Pinatubo’s eruption

It is noteworthy that the government of Philippines responded quickly to early warnings of the researchers of the Philippine Institute of Volcanology and Seismology in collaboration with the United States Geological Surveyor regarding possibility of climatic eruption of Mt Pinatubo. It resulted in a possible evacuation of several hundred households within 20 km of Mt Pinatubo region. Most of the Philippines living in the Luzon area were evacuated to various evacuation centers for their safety. The evacuation factor played a great role in saving lives and property worth million dollars. Additionally, the US also evacuated all their citizens for the Clarke Air Base situated near the mountain to other military bases while some moved to the US mainland.

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