A volcanic eruption of VEI strength 6 from a 13,000-foot-high mountain near Arequipa
On February 19, 1600, South America’s biggest volcanic eruption in all of recorded human history occurred in a mountain close to Arequipa, a city in southern Peru. Its VEI was 6, the same as Krakatau’s, and the type of eruption was also the same as Krakatau’s, a Plinian one. By that term we mean that such an eruption sends ash, smoke, and fragments of volcanic rock with terrific force high into the atmosphere, frequently as high as twenty-five miles. Places within fifteen miles of the Arequipa volcano were devastated. The neighboring states of Chile and Bolivia received thick layers of ash, as did Lima, the capital and largest city of Peru. Later, ruins revealed the details of the communities that had been smothered by ash and rock fragments, just as Pompeii had been by a similar event in the year 79. The name Plinian was given to this type of eruption in honor of Pliny the Elder, the famous Roman who was killed when Mount Vesuvius erupted, killing him and most of the people of Pompeii.
Drainage, lakes, and transportation routes were all affected because of the huge amount of material that fell on them. In addition to the human losses, the loss of farmland, vineyards, crops, livestock, and water supplies completely disrupted the economy of the area. There were no international trading links, and no manufacturing or similar occupations to which people could turn in 1600 for their survival. They depended totally on what they could obtain from the ground. Fortunately, recovery was undertaken immediately. Arequipa was rebuilt and within a few years farming activities were close to pre-eruption standards, largely the result of life being very simple. In recent times, mainly through examining underground evidence of past climates, scientists have come to see that the impact of Arequipa was far greater than local records from 1600 would suggest. It affected countries all over the world. A few scientists said that it contributed to a worldwide cooling that occurred in the summer of the year 1601, the coldest summer within the past five hundred years.
The eruption was preceded by a series of earthquakes and explosions as magma made its way upward toward the surface. The volcanic mountain that was about to explode stood more than 13,000 feet high within the upper reaches of a broad valley. It had three vents high above the valley through which gas, smoke, and pumice was about to escape. Each one of the three was huge, about 300 feet deep and over 250 feet in diameter. The setting of the mountain was equally impressive, a valley that had been carved out of an ancient volcano’s side and summit, a horseshoe shaped amphitheater that looked like a glacial cirque. It is clear from the evidence that is being uncovered at the present time that the area around Arequipa experienced numerous volcanic eruptions over the past few millions of years. In the case of the 1600 eruption, tremors were felt long before February 19. By February 15, these movements increased in both number and intensity, and this condition was maintained right up to the night of February 18. On the fateful day of the eruption there was an explosion like the noise of a cannon, followed by a big fire that scared everyone. Within an hour of the explosion, the whole surrounding region became dark as large volumes of ash and other volcanic materials fell back to earth through the atmosphere. There was little change in this continuous flow of dark material until the eruption ended on the second of April. The following list summarizes the sequence of events.
February 15 – Regular earthquakes begin
February 18 – 9 P.M.: Earthquakes increase in strength
10 P.M.: People awakened by the strength of the earthquakes
February 19 – Midday: two major quakes of intensity 11 (MM scale)
5 P.M.: Eruption began, pumice and ash falls
6 P.M.: Whole region dark with explosions every few seconds
February 20 – Explosions and ash continue all day
2 P.M.: All day was like midnight
10 inches of sand and ash fall on Arequipa
Eruption and earthquakes continue all day
February 28 – A major earthquake
March 5 – Ash fall finally stops
April 2 – Atmosphere finally cleared
A flow of heavy, hot, pyroclastic material began to appear soon after the eruption. It formed new rivers as it traveled, disrupting the natural flow of water as well as the dams that had been built on the River Tambo. It was in the neighborhood of this river that most people lived. As volcanic material fell back from the sky and was added to the surface flow, the combined mass of material rolled down the steep slopes beneath the mountain and further disrupted everything on the surface. Fire and the weight of falling material did most of the damage. Today, geologists examining the scene of the 1600 eruption are finding plenty of evidence of the event. Thick layers of ash and pumice can be seen all over the area west of the River Tambo and the city of Arequipa. It is easy to see why most of the one thousand people of the region were killed. There is a record of the experiences of a hundred people who lived in one village. It tells of stones falling from the sky with many people and animals being killed, without giving them a chance to escape. Chaos and fear had gripped everybody; they hugged one another as hot ashes were falling and burning their homes.
The people were understandably terrified by the event, mainly because of ignorance and fears over the causes of volcanic eruptions. No one knew anything about tectonic plates in 1600. Records tell of Indians praying and casting magic spells because they felt that the church was unable to do anything about the eruption. Some local people prayed on their knees all day as one of their number played a doleful lament and asked for mercy. Fear drove people to walk around their community in a sort of dazed state. Churches kept their doors open all the time. Implicit in all of these reactions was the assumption that God was responsible for what happened and, since this particular event was troublesome and harmful, he must have done it as a punishment for bad behavior. To make matters worse, the local Spanish priest had warned his people at the time of the first small earthquakes that a hit from heaven was going to come to punish them for their sins. It was a similar story more than a hundred years later when Lisbon experienced a powerful earthquake on All Saints Day. Large numbers of people were in their churches when the earthquake struck. Lisbon was a very religious city and they were convinced that the earthquake was a punishment from God.
The warning from the priest was a particularly troubling factor for the social life of the community. The conquest of the area by the Spaniards, in the previous century, had brought to this village all that was best in the world. While it came by force of arms it nevertheless represented many things that were an improvement over their former lifestyle. Arequipa and its surrounding communities had been a traditional Indian village until the Incas captured it and made it the supply center for its capital of Cuzco nearby high in the mountains. Within a century of that development, the Spaniards arrived and took full control of the area. They immediately stopped the ancient practice of sacrificing humans and animals in order to appease the gods of the mountains but now, in 1600, the natives were in a helpless situation. The church could only threaten punishment. It could not stop the eruption. The mythology of the area told them that the devil was upset because they had abandoned sacrifices so he was going to punish them. Local wizards now persuaded them to find the nicest young girls, the best animals, and the prettiest flowers and sacrifice them. During the sacrifice the first burst came from the volcano and they were covered with ash.
There were reports from ships at sea experiencing ash falls, from as far as a thousand miles, just as there had been from Lima, in northern Peru, also a thousand miles away. However, most of the ash falls happened in Bolivia and Chile because the borders of all three countries are close to the site of the eruption. In the Pacific, offshore from Peru, sailors in a British pirate ship heard the explosions and thought they were about to be attacked by a Spanish warship. A merchant sailing south from Lima was caught in a storm of ash and pumice when his ship was off the coast two hundred miles west of Arequipa. The weight of ash dragged most of his boxes overboard. If we take the immediate communities in and around Arequipa for a distance of twelve miles outward from the city, it becomes clear that more than a thousand acres were covered with sufficient ash to make them unusable for many years. One factor that is rarely mentioned is the influence of rainfall on steep slopes when all the natural drainage channels have been dislocated. Rainfall is heavy on the west side of Peru’s mountains and over the year or two following the eruption, without access to their natural channels, rainstorms washed away into the sea every movable thing on the sloping mountainside, including livestock, crops, and fish.
Volcanic eruptions along the west coast of Peru, as well as in other countries on that coast, are due to the accumulation of magma near the surface because of the subduction of the Nazca Plate beneath the continent of South America, disrupting both temperature and rock regimes deep below the surface. Peru experiences more earthquakes and volcanic eruptions than most of the countries on that coast. There are dozens of significant earthquakes every year, yet it seems that their familiarity with earthquakes and volcanic eruptions makes the people resilient, ready to start over when tragedy hits. It is an attitude similar to that found in Japan, another country well acquainted with earthquakes and volcanic eruptions. In 1784, Arequipa was hit with an earthquake that killed fifty people and destroyed almost all the buildings. Two others, in 1868 and 2001, did extensive damage. Despite the hazards, the city has grown rapidly through the years because it is located in a good agricultural area and it is strategically located for transportation. Arequipa’s population has grown from about 20,000 at the end of the eighteenth century to 600,000 today, making it Peru’s second biggest city.
The 1784 earthquake in Arequipa provided a better picture of the ways in which the Spanish overlords used local labor in the work of recovery. The records of the 1600 event do not tell us anything about relations between the Spanish and the local people. In 1784 it is clear that forced labor was the method. Spanish royalty launched their conquest of South America in order to exploit its wealth, just as the British had done in America during the colonial period, and the Spanish would learn at a later time, just as the British did, that exploitation leads to revolution if the local people are not treated fairly. In 1784, the officer in charge arranged for a forced draft of six thousand Indians from neighboring areas to be brought to Arequipa to rebuild the city. There was little difficulty in arranging this as it was a common occurrence. An arrangement for ensuring adequate labor for the mines was a similar forced draft: every Indian community had to send one-seventh of their adult male population for a year to work in the mines. The low wages they were paid did not interfere seriously with the profits that had to be sent back to Spain, even after destructive earthquakes like this one in 1784 when the city was a much bigger place than in 1600.
Fortunately, recovery from the eruption in and around Arequipa did not take too long, perhaps because the area was not highly developed and the work of restoration consisted mainly of removing ash and other volcanic debris. During the eruption, ash had been falling so fast that the mayor of Arequipa gave orders to clear the roofs to protect them from collapsing. About three feet had fallen on the city by the time the eruption began to subside. For the cleanup the Spanish Commander commandeered six hundred natives and forty soldiers to clear the ground and rebuild the homes and public buildings. The work took a few years and Arequipa became known as the white city because of the volcanic stones used in construction; they were whitish in color and very hard, unlike pumice. It seems strange to use volcanic rock as the building material for a city destroyed by a volcanic eruption. Viticulture was a well-known traditional industry of the area and a particular tragedy was the loss of grape crops as a result of the ash fall. Seventeen years after the eruption, a visitor noted that very little development of agriculture had occurred since the eruption and no evidence anywhere of a revival of viticulture.