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A traveler moving south overland through Central America gradually has his choice of routes whittled away until he finally reaches the end of the road in the swamps and forests of Darien, in Panama, where the tenuous land bridge separating the two great American continents is almost pinched out and the Pacific and Caribbean oceans almost meet. Costa Rica lies at the northern point of this apex: a pivotal region separating two oceans and two continents vastly different in character.
The region is a crucible. There are few places in the world where the forces of nature so actively interplay. Distinct climatic patterns clash and merge; the great landmasses and their offshore cousins, the Cocos and Caribbean plates, jostle and shove one another, triggering earthquakes and spawning sometimes cataclysmic volcanic eruptions; and the flora and fauna of both the North and South American realms, as well as those of the Caribbean and the Pacific, come together and play Russian roulette with the forces of evolution. The result is an incredible diversity of terrain, biota, and weather concentrated in a country barely bigger than the state of New Hampshire.
At 50,895 square kilometers, Costa Rica is the second smallest Central American nation after El Salvador. At its narrowest point, in the south, only 119 kilometers separate the Caribbean from the Pacific. Even in the north one can savor a leisurely breakfast on the Caribbean and take an ambling five-hour drive to the Pacific for dinner. At its broadest point, Costa Rica is a mere 280 km wide. On the ruler-straight eastern seaboard, barely 160 km separate the Nicaraguan and Panamanian borders. And while the Pacific coast is longer, it is still only 480 km from the northernmost tip to the Panamanian border as the crow flies.
Located between 8deg. and 11deg. north of the equator, Costa Rica lies wholly within the tropics, a fact quickly confirmed in the middle of a rainy afternoon in the middle of the rainy season in the middle of the soddeningly wet Caribbean lowlands or Talamanca Mountains. Elevation and extremes of relief, however, temper the stereotypical tropical climate. In fact, the nation boasts more than a dozen distinct climatic zones. Even ice and snow aren't unknown in cooler months atop the highest mountains.
A Backbone Of Mountains
Costa Rica sits astride a jagged backbone of volcanoes and mountain chains, part of the great Andean-Sierra Madre chain which runs the length of the western littoral of the Americas. From the Pacific coast of Costa Rica great cones and domes dominate the landscape, and one is almost always in sight of volcanoes.
The mountains begin as a low, narrow band of hills which rise from the nation's northwesternmost corner, growing steeper and broader and ever more rugged until they gird Costa Rica coast to coast at the Panamanian border, where they separate the Caribbean and Pacific zones from one another as surely as if these were the towering Himalayas.
Volcanic activity has fractured this mountainous backbone into distinct cordilleras. In the northwest, the Cordillera de Guanacaste rises in a leap-frogging series of volcanoes, including Rincón de la Vieja, and Miravalles, whose steaming vents have been harnessed to provide geothermal energy. To the southeast is the Cordillera de Tilarán, dominated by Arenal, one of the world's most active volcanoes. Rising higher yet to the east is the Cordillera Central, with four great volcanoes--Poás, Barva, Irazú and Turrialba. Together, these three cordillera form the Central Highlands, within whose cusp lies the Meseta Central, an elevated plateau ranging in height from 900 to 1,787 meters. To the south of the valley is the Cordillera Talamanca, an uplifted mountain region that tops out at the summit of Cerro Chirripó (at 3,797 meters, Costa Rica's highest peak).
All roads radiate out from the Meseta Central, the heart and heartbeat of the nation. This rich agricultural valley is cradled by the western flanks of the Cordillera Talamanca to the south, and to the north and east by the fickle volcanoes of the Cordillera Central. San José, the capital city, lies at its center. At an elevation of 1,150 meters, San José and neighboring Alajuela, Cartago, and Heredia enjoy year-round temperatures above 70deg. F, reliable rainfall, and rich volcanic soils--major reasons why almost two-thirds of the nation's population of 3,087,000 live in the valley.
The Meseta Central--which measures about 40 km north to south, 80 km east to west--is divided into two separate valleys by the low-lying crests of La Carpintera Mountains, which rise a few miles east of San José. Beyond lies the somewhat smaller Cartago Valley, at a slightly higher elevation. The Carpinteras mark the Continental Divide. To the east the turbulent Reventazón--a favorite of whitewater enthusiasts--slices through the truncated eastern extreme of the Cordillera Central and tumbles helter-skelter to the Caribbean lowlands. The Río Virilla exits more leisurely, draining the San José Valley to the west.
The broad, pancake-flat, wedge-shaped northern lowlands are cut off from the more densely populated highlands by a languorous drape of virtually impenetrable hardwood forest which only the most accomplished outdoor types can penetrate without local guides. The low-lying plains or llanuras, which only in a few places exceed 480 meters above sea level and which comprise one-fifth of the nation's land area, extend along the entire Caribbean coast and along the full length of the San Juan River, whose course demarcates the Nicaraguan border. The coastal plains are not immune to the geological processes at work in Central America, however, and tiny volcanoes stud the landscape, easing their way up through the treetops.
Inland, banana plantations and swatches of newly cleared farmland give way to pleats of green velveteen jungle ascending the steep eastern slopes of the central mountains, which run along a northwest-southeast axis, forming the third side of the wedge. Numerous rivers drop quickly from the mountains to the plains, where they snake along sluggishly and provide the main means of transport: riverboat and canoe. Beautiful white- and black-sand beaches line the Caribbean coast, which has few indentations and sidles gently south as sleek as a yardstick.
Beaches are a major calling card of the Pacific coast, which, unlike the homogeneous Caribbean seaboard, is deeply indented with multiple bays and inlets and two large gulfs: the Gulf of Nicoya (in the north) and Golfo Dulce (in the south), enfolded by the hilly, hook-nosed peninsulas of Nicoya and Osa, respectively. The interior mountains tilt precipitously toward the Pacific, coming closer to the ocean than on the Caribbean side, and the slender coastal plain is nowhere more than a few kilometers wide. Two broad fertile valleys break this rule, separating the Nicoya and Osa peninsulas from the mainland. North of the Gulf of Nicoya, the coastal strip widens to form a broad lowland belt of savannah--the Tempisque Basin--drained, appropriately, by the Tempisque River, and narrowing northward until hemmed in near the Nicaraguan border by the juncture of the Cordillera de Guanacaste and rolling, often steep coastal hills that follow the arc of the Nicoya Peninsula.
Of growing importance to the national economy is the narrow, 64-km-long intermontane basin known as the Valle de El General, which runs parallel to and nestles comfortably between the Cordillera Talamanca and the coastal mountains--Fila Costeña--of the Pacific southwest. The rivers General and Coto Brus and their many tributaries have carved a deep, steep-sided trough, long isolated from the rest of the nation. The construction of the Pan-American Hwy. through the valley in the 1950s brought thousands of migrant farmers and their families in its wake.
Costa Rica lies at the boundary where the Pacific's Cocos Plate, a piece of the earth's crust some 510 km wide, meets the crustal plate underlying the Caribbean. The two are converging as the Cocos Plate moves east at a rate of about four inches a year. It is a classic subduction zone in which the Caribbean Plate is forced under the Cocos, and one of the most dynamic junctures on earth. Central America has been an isthmus, a peninsula, and even an archipelago in the not-so-distant geological past. It has therefore been both a corridor and a barrier to landward movements, and it has been an area in which migrants have flourished, new life forms have emerged, and new ways of life have evolved. Yet a semblance of the Central America we know today became recognizable only in recent geological history. In fact, Costa Rica has one of the youngest surface areas in the Americas--only three million years old--for the volatile region has only recently been thrust from beneath the sea.
In its travels eastward, the Cocos Plate gradually broke into seven fragments, which today move forward at somewhat different depths and different angles. This fracturing and competitive movement is the cause of the frequent earthquakes Costa Ricans have to contend with (during one two-month period in 1989, seismologists recorded more than 16,000 tremors in Costa Rica; most were imperceptible to people, but 16 registered above 4.0 on the Richter scale). The forces that thrust the Cocos and Caribbean plates together continue to build inexorably.
From insignificant tremors to catastrophic blockbusters, most earthquakes are caused by the same phenomenon: the slippage of masses of rock along earth fractures called faults. Rocks possess elastic properties, and in time this elasticity allows rocks to accumulate strain energy as tectonic plates or their component pieces jostle past each other. For years friction contains the strain and holds the rocks in place. But eventually, as with a rubber band stretched beyond its breaking point, strain overcomes frictional lock and the fault ruptures at its weakest point. Suddenly, the pent-up energy is released in the form of seismic waves--the earthquake--that radiate outward in all directions from the epicenter, the point of rupture. This rupturing lasts from a fraction of a second to many minutes for a major earthquake. Pressure waves traveling at five miles per second race from the quake's epicenter through the bedrock, compressing and expanding the ground like an accordion. Following in their wake come waves which thrust the earth up and down, whipping along at three miles per second.
For Costa Ricans the bad news is that the most devastating earthquakes are generally associated with subduction zones, where one tectonic plates plunges beneath another. Ocean trench quakes off the coast of Costa Rica have been recorded at 8.9 on the Richter scale and are among history's most awesome, heaving the sea floor sometimes by scores of feet. These ruptures often propagate upward, touching off other lower-magnitude tremors in a system of overlapping cracks in rock called imbricate faults, as happened when the powerful 7.4 quake struck Costa Rica on 22 April 1991.
Costa Rica lies at the heart of one of the most active volcanic regions on earth. The beauty of the Costa Rican landscape has been enhanced by volcanic cones--part of the Pacific Rim of Fire--that march the length of Central America. Costa Rica has seven of the isthmus's 42 active volcanoes, plus 60 dormant or extinct volcanoes. Some have the look classically associated with volcanoes--a graceful symmetrical cone rising to a single crater. Others are sprawling, much-weathered mountains whose once-noble summits collapsed into huge depressions, called calderas. Still others have smooth shield-shaped outlines with rounded tops pockmarked by tiny craters, such as on Cocos Island.
Visitors seeking to peer into the bowels of a rumbling volcano can easily do so. The reward is a scene of awful grandeur, like the fires of Milton's hell. Atop Poás's crater rim, for example, you can gape down into the great well-like vent where pools of molten lava bubble menacingly--with diabolical, gut-wrenching fumes of chlorine and sulfur, and explosive cracks, like the sound of distant artillery, for good effect.
Several national parks have been created around active volcanoes, with accommodations, viewing facilities, and lectures and guided walks to assist visitors in understanding the processes at work. A descriptive map charting the volcanoes is published by the Vulcanological and Seismological Observatory of Costa Rica at the National University in Heredia, which monitors volcanic activity throughout the nation (Libreria Lehmann and Libreria Trejos, in San José, may sell the map).
In 1963, Irazú (elev. 3,412 meters) broke a 20-year silence to begin disgorging great clouds of smoke and ash. The eruptions triggered a bizarre storm which showered San José in five inches of muddy ash and snuffed out the 1964 coffee crop, enriching the Meseta Central for years to come. The binge lasted for two years, then abruptly ceased. Poás (elev. 2,692 meters) has been particularly virulent during the past 30 years. In the 1950s, the restless four-mile-wide giant awoke with a roar after a 60-year snooze, and it has been huffing and puffing ever since. Eruptions then kicked up a new cone several hundred feet high. Two of Poás's craters now slumber under blankets of vegetation (one even cradles a lake), but the third crater belches and bubbles persistently. In 1989, a spate of intense eruptions and gas emissions forced Poás Volcano National Park to close (local residents were even evacuated), and the volcano is constantly monitored for impending eruptions.
A more spectacular light-and-sound show is given by Arenal (elev. 1,624 meters). Following a four-century-long Rip van Winkle-like dormancy, this 4,000-year-young juvenile began spouting in 1968, when it laid a four-square-mile area to waste. Arenal's activity, sometimes minor and sometimes not, continues unabated. Though currently more placid, Miravalles, Turrialba, and Rincón de la Vieja, among Costa Rica's coterie of coquettish volcanoes, also occasionally fling fiery fountains of lava and breccia into the air.
The type of magma that fuels most Central American volcanoes is thick, viscous, and so filled with gases that the erupting magma often blasts violently into the air. If it erupts in great quantity, it may leave a void within the volcano's interior, into which the top of the mountain crumbles to form a caldera (from the Portuguese word for caldron). Irazú is a classic example. Irazú's top fell in eons ago. Since then, however, small eruptions have built up three new volcanic cones--"like a set of nesting cups," says one writer--within the ancient caldera.