A sobering view of a Two-toed Sloth as it makes its way along utility lines on our way to Monteverde Preserve. This is what can happen to animals faced with disappearing habitat.
Volcanoes have a huge impact on humanity and all organisms by both enhancing and destroying life. The mechanics governing volcanoes help to explain their patterns and are important in the overall understanding and appreciation of these miraculous structures. Historically, volcanoes on a global scale have been seen as menacing, violent objects as well as bearers of new life, although the former is more common. They alter the physical and ecological environment and have both positive and negative effects. Volcanic activity is a defining characteristic of some areas of the world. The Caribbean is not currently one of these areas, but there have been some significant volcanic events in the Caribbean’s past. The main historically active sites of the Caribbean region, as well as sites of possible future activity will be explored here.
An understanding of the mechanics of volcanoes is necessary for a holistic approach to predicting their activity. First, it is important to know that the earth is made of three primary layers: the core, the mantle, and the crust respectively from inside out. However, the earth is not just three distinct or discrete layers, but rather interacting layers and “plates”. Molten magma in the mantle moves in what are known as convection currents, pushing the proposed plates of the plate tectonic theory (Figure 1). This theory asserts that the outer portion of the earth is made of plates composed of either primarily land, primarily ocean, or both land and ocean (Figure 2). It also further divides the three primary layers of the earth. The crust and very top of the mantle are together known as the lithosphere (Figure 3). This layer is thin, yet solid and is the layer of the plates (Montgomery, 46). The next layer below the lithosphere is the asthenosphere and is thicker and softer (Montgomery, 46). The plastic asthenosphere layer allows the lithospheric plates to move over top of it.
There are two major interactions between adjacent plates that commonly cause volcanoes to form (Figure 4). The first is when two bordering plates colide forming what is known as a convergent margin, or a subduction zone (Decker & Decker, 9). In this case, the denser plate (usually the oceanic plate if the other is mostly land) slides beneath the less dense plate. In this setting, the plate sliding beneath the other is transformed as it is forced downward through the mantle towards the crust and is re-melted into magma. In this case, volcanic mountain ranges are formed on one side by the crust being lifted (Erickson, 3). The second plate interaction is when two plates move away from each other, known as a divergent margin, or a rift (Decker & Decker, 10). This usually occurs between two oceanic plates and thus is far underwater. At divergent boundaries, new additions are added to the plates from magma rising from the lower layers of the earth in the space between the spreading plates (Erickson, 2). There is also a third type of plate interactions in which two plates slide past each other; however, volcanoes are not common at these plate boundaries.
A number of volcanic monitoring processes can be used at and near these interacting plate boundaries. The simplest methods involve utilizing physical and biological indicators. Examples of physical indicators include visible warning signs of eruptions such as bulging, gas release, and/or heated waters in surrounding areas of volcanoes (Montgomery, 112). Animals can sometimes serve as biological indicators. They often exhibit very strange behavior just prior to volcanic eruptions (Montgomery, 112). These two methods of observation can be used along with more scientific methods of predicting volcanoes. Monitoring stations are set up all around volcanoes to get multiple readings of physical and chemical signals (Bourseiller & Durieux, 168). Seismicity, or the waves of motion associated with volcanoes, is the most common signal measured (Bourseiller & Durieux, 168). These waves radiate out from their origin and are thus detected by seismographs at the surrounding monitoring stations (Bourseiller & Durieux, 168).
Some of the effects of volcanoes, and most commonly the characteristics that they are associated with, can be deadly. First, volcanoes produce lava. Although this is the most popular effect that people link volcanoes with, it is not usually the most harmful. More properly, the lava explosions are called pyroclastic flows. There also are many gases that volcanoes produce including carbon monoxide, carbon dioxide, sulfur dioxide, hydrogen sulfide, and cyanide (Erickson, 48). Some of these are suffocating gases and some are also toxic to organisms. In both cases, these gases can cause great loss of life. Additionally, volcanoes can produce what are known as lahars, or great mudflows (Erickson, 62). These are usually more harmful than lava because they can travel much faster than the viscous or slow moving lava. Also, nuée ardentes, or explosions of hot ash and gas, may be produced (Erickson, 174). Nuée ardente literally means “glowing cloud” (Decker & Decker, 92). Nuée ardentes are usually the most feared effects of volcanic eruptions because of the great damage they cause, especially to humans (McQuire & Kilburn, 126). With all of these harmful effects, organisms are displaced and killed as their habitats are destroyed. Thus there is a close ecological link between volcanoes and organisms.
Aside from all the negative effects that volcanic eruptions can have, there are certain positive effects of these structures. For example, the land near volcanoes is often more fertile than other areas. As the soils of old volcanic eruptions begin to weather, nutrient and mineral rich soil is produced (Johnson, 127). This allows for a wide variety of plants and animals to inhabit these areas that might otherwise not be found in these regions (Johnson, 117). Also, many valuable ores such as gold, silver, and platinum are created by volcanoes (Johnson, 117). Volcanoes have also played a major role in creating the current atmosphere of our world with the gases they release (Johnson, 117).
Many of the features of volcanoes globally can be seen specifically within the Caribbean. The Caribbean plate has both convergent, or subduction, and divergent boundaries with its neighboring plates (Montgomery, 49). Within the Caribbean plate, there exists seventeen active volcanoes and volcanic fields (McQuire & Kilburn, 125). Sixteen volcanoes form the island arc of the Lesser Antilles of the Caribbean. These volcanoes are characterized by nuée ardentes and several other specific volcanic effects (McQuire & Kilburn, 126, 128). McQuire and Kilburn wrote:
“Unlike the runny lavas that characterize eruptions at oceanic volcanoes, such as Hawaii and Iceland, those of the Lesser Antilles volcanoes –where Atlantic Ocean floor is being subducted beneath the Caribbean Plate- are glutinous and slow moving. Consequently, they rarely form flows, but instead pile up over the eruptive vent to form huge and typically unstable domes. Often, gigantic spines of sticky lava are pushed skyward from the surface of a lava dome, before collapsing and disintegrating to form pyroclastic flows” (128).
There are only a few large eruptions known of the Lesser Antilles, however, there are only volcanic records since 1630 (McQuire & Kilburn, 126). There have been only 33 total eruptions since 1690, the year that the first eruption was recorded (McQuire & Kilburn, 126). This first eruption was the volcano La SoufriŹre on the island of Guadeloupe, the largest island of the Lesser Antilles (McClelland et al., 541). The majority of the eruptions since 1690 have been at La SoufriŹre of Guadeloupe, La SoufriŹre of St. Vincent, and Mont Pelée of Martinique (McQuire & Kilburn, 126). These three sites are known among “the world’s 101 most notorious volcanoes” (Decker & Decker, 284). La SoufriŹre of St. Vincent, La SoufriŹre of Guadeloupe, and Mont Pelée of Martinique are all the type of volcanoes known as stratovolcanoes (Decker & Decker, 284). Stratovolcanoes are steep volcanic cones, built up by the materials of volcanic eruptions over time (Decker & Decker, 312). These are also known as composite volcanoes because they are made of many types of materials layered upon each other (Montgomery, 103).
The seventeenth Caribbean volcano, outside of the Lesser Antilles is the submarine volcano known as “Kick ‘em Jenny” near Grenada (McQuire & Kilburn, 126). This volcano has been very active within the recent past, as seismic monitoring has detected (McClelland et al., 554). “The enigmatically-named submarine volcano –Kick ‘em Jenny- has erupted 10 times since the start of World War II, and twice in the last nine years” (McQuire & Kilburn, 126). Grenada inhabitants worry that Kick ‘em Jenny might collapse, which could lead to other problems including tsunamis (McQuire & Kilburn, 126). Kick ‘em Jenny is certainly a site to watch for volcanic activity in the Caribbean’s future.
The most well known of these seventeen is Mont Pelée, or the Bald Mountain, on the island of Martinique (McQuire & Kilburn, 124). This is the most famous because of its great eruption of 1902 which had virtually complete destruction of the town of St. Pierre (Johnson, 40). Prior to this eruption, St. Pierre was viewed as an excellent place to live with no danger or possibility of an eruption. The town consisted of around 31,000 people; only four of these 31,000 survived the massive eruption (McQuire & Kilburn, 124)!
The town was not concerned prior to the eruption because it had been exposed to some slight activity in 1792 and 1851 (McQuire & Kilburn, 125). Therefore, they ignored some volcanic effects that might have otherwise served as warning signs or precursors. For example, slight trembling and the smell of sulfur were overlooked by St. Pierre residents (McQuire & Kilburn, 125). Additionally, one week before the eruption, a black cloud covered the town and a lake that had been dry filled with scalding water (Johnson, 40). The people finally began to acknowledge the signs after a number of human and animal deaths due to poisonous snakes that descended from Mont Pelée attempting to escape the volcano’s wrath (Johnson, 40).
The eruption began in the early morning of May 8th, when volcanic gases and steam decimated the town of St. Pierre (McQuire & Kilburn, 125). The nuée ardente of this eruption is what killed nearly all of the town’s inhabitants. “The flesh of some 29,000 human beings was instantly boiled, with the vapourisation of body fluids causing organs to explode and skull sutures to pop apart. At the same time, however, clothing was often untouched, indicating that there was insufficient time for clothing to ignite” (McQuire & Kilburn, 126). There has since been a type of eruption named after this incredible event; Pelean eruptions, as they are called, are characterized by the formation of a summit dome (Johnson, 76). Summit domes are “hemispherical, rubbly piles of very thick, sticky lava that ooze from the eruptive vent after gas-rich lava has been expelled” (Johnson, 76). These summit domes are what produce the nuée ardentes and thus define Pelean eruptions (Johnson, 76).
The eruption of Mont Pelée was certainly the greatest event in Caribbean volcanism, as well as the greatest worldwide, in terms of total deaths, of the twentieth century (Decker & Decker, 267). It was so influential that it inspired one geologist, Thomas Jagger, to devote his life to studying volcanoes (Johnson, 41). Others were also moved by this great eruption. Alfred Lacroix started the first observatory at Mont Pelée in 1903, just a year after the massive eruption (Bourseiller & Durieux, 166). The observatory was shut down for a number of years after its 1903 grand opening due to volcanic inactivity, but was later permanently reopened in 1935 (Bourseiller & Durieux, 166). Lacroix also promoted the observatory of La SoufriŹre that was built in 1950 (Bourseiller & Durieux, 166).
From the impressive eruptions of Mont Pelée and others, humans have learned a great deal. Most importantly, humans have learned to not avoid the precursors of volcanic activity, but rather acknowledge and utilize them to minimize deaths. Humans are now able to better predict volcanic eruptions with the advanced technology of today’s society. It is certain that over time, the methods of predicting volcanic eruptions will improve. Although these incredible, yet destructive natural wonders will never cease or be tamed, monitoring practices can be used and lives can be saved. Caribbean and other global volcanoes have a promising and unknown future of activity ahead of them.
Bourseiller, Philippe and Durieux Jacques. Volcanoes. New York: Harry N. Abrams,
Decker, Barbara and Robert Decker. Volcanoes. New York: W.H. Freeman & Company,
Erickson, Jon. Quakes, eruptions, and other geological cataclysms. New York, NY: Facts
On File, 1994.
Johnson, Carl. Fire on the mountain. San Francisco, CA: Chronicle Books, 1994.
McClelland, Lindsay, Tom Simkin, Marjorie Summers, Elizabeth Nielsen, and Thomas
Stein. Global Volcanism 1975-1985. New Jersey: Prentice Hall, 1989.
McQuire, Bill and Christopher Kilburn. Volcanoes of the world. San Diego, California:
Thunder Bay Press, 1997.
Montgomery, Carla W. Environmental Geology. Boston: McGraw-Hill Companies, Inc.
Figure 1, Taken from: Erickson p. 7
Figure 2, Taken from: Montgomery p.49
Figure 3, Taken from Montgomery p. 48
Figure 4, Taken from: Decker p.10
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