Visit Your Local PBS Station PBS Home PBS Home Programs A-Z TV Schedules Watch Video Donate Shop PBS Search PBS
SAF Archives  search ask the scientists in the classroom cool science
on the islands

geography & geology



environmental threats

cyber field trip
for students
for teachers
web resources
galapagos homepage
Destination: Galapagos Islands Cyber Field Trip

The Geography and Geology of the Galapagos Islands

By clicking on the linked words, you can also learn more about some of the scientific terms used frequently throughout this site.

View from Isabela; photograph by Silvia SiegelThe Galapagos Islands are an archipelago consisting of some 16 islands and numerous islets scattered over an area of nearly 36,000 square miles around the Equator. Each major island, with the exception of the largest island, Isabela, consists of a single large shield volcano. Isabela was formed from six volcanoes joined above sea level. The total land area of all the islands, islets and rocks that form the Galapagos Islands is about 3,028 square miles, with Isabela making up more than half the total land area, at 1,700 square miles. The islands all rose from the ocean floor as the tops of volcanoes, possibly during the Pliocene era, and have never been connected by land to any mainland area. Today, the Galapagos Islands remain one of the most active oceanic volcano areas on Earth.

Lava Flow on Santiago; photograph by Silvia SiegelJust as the extraordinary wildlife of the Galapagos Islands is critical to the study of biology, the unique geology of the islands has implications for the whole planet. In geological terms, the Galapagos Islands are quite young, probably no more than five million years old. Some of the westernmost islands, which are the most volcanically active, may only be hundreds of thousands of years old and are actually still forming. Lava flow on Santiago; photograph by Silvia SiegelFernandina, for example, at its current rate of activity, may one day expand to meet the shores of Isabela, creating a single, large island. As these amazing changes take place, scientists can observe the effects of the tides, wind and weather on the process. They are then better able to define the impact of the environment on both the Galapagos Islands and, by extension, the Earth. More importantly, these studies can help scientists develop ways to protect the environment in our ever-changing world.

Though the islands are now quite isolated, at 600 miles from the nearest mainland, some biologists believe that the Cocos Ridge, which runs under the sea and extends almost the entire distance from Costa Rica to the northern islands, was once a land bridge. These biologists use this theory to explain how some of the life on the Galapagos Islands arrived there, but it has not yet been proven. Although many species of flora and fauna that thrive on the Galapagos Islands resemble those native to South America, they have evolved so extensively in isolation that they now appear very different from their mainland ancestors.

There are four main ecosystems in the Galapagos Islands, which have been formed over time by wind patterns and differences in elevation. The first ecosystem is made up of arid lowlands and open forests of enormous cacti; the second consists of Cactus from Santiago; photograph by Silvia Siegelsubtropical forests; the third, found at higher elevations, is composed of moist, dense forests; and treeless upland areas covered with ferns and grasses make up the fourth. Goats, pigs, and other introduced species left by 19th century sailors to multiply on the islands and serve as a source of fresh meat on later visits eventually destroyed much of the native vegetation on many of the islands. The remaining areas consist of little more than bare, hardened lava, which has formed cliffs and jagged points of land along the coasts. Volcanic activity has produced several thousand calderas and cones throughout the archipelago, the largest of which may be found on the islands of Isabela and Fernandina. These unusual landforms give the landscape of some islands an almost lunar quality.

Today, there are human settlements on four of the major islands. Tourism is the main business, though cattle and coffee are two popular exports. Both legal and illegal commercial fishing are on the rise in the waters off the Galapagos Islands, despite laws created in recent years to protect the wildlife sanctuary.


Scientific American Frontiers
Fall 1990 to Spring 2000
Sponsored by GTE Corporation,
now a part of Verizon Communications Inc.