Final - Landforms, Geology, and Natural Disasters of Costa Rica

This discussion topic submitted by at 5:46 pm on 5/18/01. Additions were last made on Saturday, May 4, 2002.


Janelle Engel
Geology 499
May 16, 2001


Landforms, Geology, and Natural Disasters of Costa Rica

Tourism in Costa Rica today has quickly become an essential part of the country’s economy. People travel from all over to visit the archeological sites, relax on the beautiful beaches, or conduct research in one of the many ecosystems of the “rich coast”. The country only covers about 19,653 square miles, which is roughly the size of West Virginia, yet, a variety of different landscapes exist within this small area, including mountain ridges, river valleys, rainforests, and coastal lowlands and beaches (Sawyer 13). The geology of Costa Rica is one of the most interesting and influential qualities of the country because it determines everything from landforms, to wildlife, to natural disasters there.
Topography
Costa Rica can be divided into four geographical areas: the tropical lowlands on the Pacific and Caribbean coasts, the North Central plains, the Central valley, and the Northwest peninsula (Infocostarica). The lowland area covers much of the northern part of the country, and is criss-crossed with rivers flowing down from the highlands. The terrain here includes scattered hills, but is mostly flat plains. These plains continue from the north up to the Caribbean coast and can account for about 1/5 of Costa Rica’s total land area (Nelson 45). Dense tropical rain forests and beautiful beaches line both the Caribbean and Pacific coasts. The Pacific coast has a varied topography, with mountain peninsulas and scattered narrow beaches, while the Caribbean is generally flat.
Most of the cities in Costa Rica and the bulk of the population are located in the highland Central valley, called the Meseta Central, which is a temperate area between 1000 and 4500 meters above sea level (Nelson 74). “Two intermittently active volcanoes of the Cordillera Central overlook the Meseta Central from the north and northeast” (Nelson 75). These peaks are a part of the Cordillera Central, one of the four mountain ranges, running from northwest to southeast in Costa Rica. The others are the Cordillera de Tilaran, the Cordillera de Talmanca, and the Cordillera de Guanacaste (Sawyer 109).
Such a difference in elevation between the mountain peaks in the center of the country and the lowlands near the shore is one reason for the radically diverse ecosystems and wildlife found in the different areas of Costa Rica. Elevation determines critical biotic factors of the environment such as the amount of rainfall an ecosystem will receive and the average mean temperature of the area. Nelson (77) estimates that “for every 1000 meters of altitude, the mean annual temperature will change 5 degrees Celsius”.
Geology
Geologically, Costa Rica is very young, emerging from under the ocean only 50 million years ago (Garrigues). Plate tectonics play a major role in the geology of Central America and it is an essential factor when explaining the geologic history of Costa Rica. The theory of plate tectonics is based on the notion that the earth’s crust (the uppermost layer) is divided into numerous sections called plates, which are supported by an unstable substance below. Currently, “Costa Rica’s land mass is positioned at the western edge of the Caribbean plate, which is moving westward and overriding the Cocos plate located in the Pacific ocean” (SuperSite). At times, “the gravity induced sinking of cool, dense materials at the plate margins and sea-floor spreading at mid-ocean ridges can cause relative motion between adjacent plates” (SuperSite). These movements greatly affect the topography of the land, and sometimes result in earthquakes and volcanoes.
As the oceanic plate (Cocos) collides with the continental plate (Caribbean), it is subducted under the continental plate, being exposed to increased heat and pressure, and will eventually turn into molten rock. When the pressure finally builds up too much, the lava and steam will move back upward toward the surface. This is happening right beneath the western edge of the Caribbean plate, due to “the angle of the downward thrust to the east of the submerged plate” (Garrigues). Volcanoes form as the result. The earliest volcanoes were under water, but as layer after layer cooled into rock, the mountains grew higher and eventually emerged above the surface of the ocean. A chain of volcanic islands formed between Guatemala and Columbia, where before there had been open ocean. As the volcanoes continued to erupt, the space between the islands filled in and eventually turned into the huge landmass that is Central America (Garrigues 1996). Additionally, while the Cocos plate submerges even further, sea-floor sediments are scraped off of the edge of the subduction zone, and turn into wedges of sedimentary rocks that are piled upon the coast of the growing continent (Janzen 89).
Natural Disasters
Natural disasters can be separated into two major groups: (1) meteorological phenomena, such as hurricanes, storms, droughts and floods; and (2) geophysical activity, such as earthquakes, volcanic eruptions, landslides, and mudslides (Uribe and Sakai). The main hazards for Costa Rica are earthquakes and volcanic eruptions, due to the geologically active land area. Severe flooding is also a problem because of the vast amounts of rainfall received there. Although it is possible for hurricanes to hit Costa Rica, it is unlikely because the country is south of the area where the hurricanes usually occur. Even if a hurricane is not hitting Costa Rica directly, the outskirts of a storm could inflict serious damage upon the country, such as mass flooding due to heavy rains and high waves.
Currently, the Cocos and Caribbean plates are moving at a rate of about 1 to 4 inches per year (SuperSite). The transition is not smooth when the plates are sliding by one another: pieces of the earth can snag and break loose intermittently, producing earthquakes. The last serious seismic catastrophe occurred in April 1991, measuring 7.1 on the Reichter scale (Garrigues). The Atlantic zone of the country, its buildings, roads, and even coral reefs suffered great damage, but some areas of the country were not affected at all. “This earthquake killed 27 people, injured 400, and left 13,000 homeless in the Limon (Atlantic) province” (Infocostarica). Earthquakes also cause problems when landslides occur after the shake. Other significant earthquakes include the one that destroyed much of Cartago in 1910 and the series of moderate earthquakes that hit San Jose in 1990. These large-scale quakes rarely occur, while harmless tremors are not unusual.
As mentioned above, volcanoes erupt when heat and pressure turn solid rock into a molten form. The pressure from the gas and heat builds up until the lava must burst out the top. Costa Rica is a very volcanically active spot, being located within the Ring of Fire, which is made up of geologically active sites all around the rim of the Pacific Ocean. The country contains 60 dormant or extinct volcanoes, as well as 7 active volcanoes: Arenal, Irazu, Poas, and Rincon de la Vieja being a few of the most well known (Global Volcanism). The last big eruption occurred in 1963 at Irazu. After being dormant for 20 years, clouds of ash and smoke suddenly erupted from the volcano and continued for two years (Global Volcanism)! “ It sent tephra and secondary mudflows into cultivated areas, caused at least 40 deaths, and destroyed 400 houses and some factories” Global Volcanism). Irazu is the highest volcano in Costa Rica, and is quite active with at least 23 eruptions since 1723. One Costa Rican native recalls stories from her parents and grandparents about the eruption: “they had to walk around carrying handkerchiefs to breath in, and sweep the sidewalks and roof everyday so it would not collapse under the weight of ash and mud” (Infocostarica).
For most of historic time, Arenal volcano was a dormant stratovolcano, which is the type that “comprises 60% of volcanoes and is characterized by eruptions of andesite and dacite - lavas that are cooler and more viscous than basalt” (SuperSite). These more viscous lavas allow gas pressures to build up to high levels; therefore these volcanoes often suffer explosive eruptions. Up until early 1963 there had always been some young deposits on the slopes of Arenal, but it had not erupted in historic time (SuperSite). In July later that year, however, Arenal produced an explosive eruption of hot avalanches and ejected blocks that devastated the west side of the volcano and killed 78 people Infocostarica). Arenal has been continuously active since 1963, with strombolian eruptions (“eruptions characterized by jetting of clots or fountains of fluid basaltic lava from a central crater”) occurring at intervals of several minutes to hours (Global volcanism).
Floods in Costa Rica are not the ordinary leaking basement variety. During the rainy season, the land accumulates up to 100 inches of rain per year and has been known to produce raging rivers that turn into avalanches of tree trunks and stones. In Spanish they call this dangerous phenomenon ‘cabezas de agua,’ meaning ‘heads of water’ (Incostarica). Floods such as these can ruin crops, homes, and even cause deaths.
Although these natural disasters have a major impact on people living in Costa Rica, much is being done to lower the risk. There is an action group called Coordination Center for the Prevention of Natural Disasters in Central America (CEPREDENAC) and their objectives state:
“The Center will promote and coordinate the international cooperation, the exchange of information, experience, technical and technological advice in matters of prevention in order to reduce the natural disasters, and thus contribute to the improvement in decision making about planning and management that will benefit the Central American area.”
Also, the private industry is helping out by offering new technology to ensure that buildings are stable during earthquakes, eruptions, flooding, and landslides, such as Quake-proof Adobe Housing. Researchers like the International Development Research Center are making efforts to learn all they can about these natural phenomenons so they can find the best way to protect people and property from damages (IDRC).

Works Cited

Nelson, Harold D. Costa Rica: A Country Study. American University:Washington DC, 1983.

Janzen, Daniel J. Costa Rican Natural History. University of Chicago Press:
Chicago, 1983.

Sawer, John, O. Vegetation of the life zones in Costa Rica. The Indiana Acadmy of Science, Indiana, 1971.

Costa Rica
Richard Garrigues 1996.
http://www.angelfire.com/bc/gonebirding/geoclime.html

The Costa Rica SuperSite

Copyright 1997-1999La Nación S.A.
Web Design by Inter@merica S.A.
http://www.incostarica.net/

Constitution Agreement of the Coordination Center for the Prevention of Natural Disasters in Central America (CEPREDENAC)
http://www.cepredenac.org/en/agreemnt.htm

Global Volcanism Program
http://www.volcano.si.edu/gvp/volcano/region14/costaric/irazu/var.htm#index

International Development Research Center
http://www.idrc.ca/adventure/disaster.html


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