Biology Reference
In-Depth Information
because of this, there have been numerous studies on the geology of the
Central Andes. Field experiences associated with these studies are vividly
recounted by Simon Lamb in
Devil in the Mountain
(2004).
Names of the physiographic provinces differ according to country, but
they consist generally of a coastal plain rising to about 1000 m elevation;
the Andes Mountains with the Cordillera Oriental, Cordillera Occidental,
and an intervening valley or a high plateau called the Puna in Peru and the
Altiplano in Bolivia. The eastern slopes are called the Yungas, and below is
the Oriente, or Amazon lowlands. It is a tectonically active region, and there
are more volcanoes in Ecuador than in any other country in South America.
Among the sixty-fi ve active volcanoes, Pichincha has erupted fi ve times in
the last fi ve hundred years, and in four of these eruptions the capital city
of Quito was nearly destroyed. Humboldt, traveling through the region be-
tween 1799 and 1804, named the two cordilleras the “avenue of volcanoes.”
The most recent eruption of Pichincha was in October and November 1999.
About 950 km to the east in the Pacifi c Ocean are the Galápagos Islands,
administered by Ecuador. The Humboldt Current is diverted westward by
the southeast trade winds and by the coastal confi guration of northern Peru
and Ecuador; thus, the climate of the Galápagos Islands is relatively cool
(21°C-26°C May through February, 28°C March and April). Darwin made
observations on the fi nches and other organisms that showed the effect of
geographic (reproductive) isolation, and this was a key component in his
formulating the theory of evolution. The Galápagos Islands are presently
the site of a beleaguered biological preserve. The islands arise over a hot
spot between the Cocos and Nazca plates (Hoernle et al. 2002), and the
outpourings of basalt may have formed the fl oor of the Caribbean Basin as
it opened in the Late Cretaceous and early Tertiary. Also offshore is a zone
of high rainfall and weather instability called the Intertropical Convergence
Zone (ITCZ), and its annual meandering north to south is a major factor
in determining the equatorial climates of the New World. In January and
February it moves south from near the equator to 2°S-3°S, and in June and
July it moves to about 9°N. Its passage over the different regions brings the
characteristic rainy seasons. In Peru, the Central Andes reach a height of
6768 m at Huascarán, where in 1970 ice from the mountain loosened by an
earthquake killed nearly 40,000 people in the nearby villages.
Important contributions to the study of tropical paleoclimates have been
made in Peru by Lonnie Thompson based on cores taken through the annu-
ally layered ice of the Quelccaya ice cap (13°S, 5670 m elevation). The cores
reveal signifi cant fl uctuations in temperature and precipitation during the
late Pleistocene even at this near-equatorial latitude (chap. 8). One conse-
