Galapagos Islands geology

The Galapagos are a group of volcanic islands located above a hot spot near the intersection of the Nazca and Cocos tectonic plates.  The dominant type of volcano found on the islands is the shield volcano, some of which contain huge calderas.  Historically recent volcanism has occurred on Alcedo, Cerro Azul, Fernandina, Floreana, Marchena, Pinta, Santiago, Sierra Negra, and Wolf volcano. 

Some islands, such as Santa Cruz and San Cristobal, have been active in recent geologic time, yet also show evidence of volcanism occurring as far back as over two million years ago. Galapagos are one of the world’s most active volcanic areas, with over 50 eruptions in the last 200 years. The largest island, Isabela, is made up of six volcanoes which have flowed into each other, filling the Pacific gap between them.

Fernandina has erupted on a regular basis, every 4-5 years since 1968, with the last eruption being in 1995 when lava flowed into the sea, also Cerro Azul volcano on Isabella has erupted regularly.

Vegetation zones

Pampa Zone: There are virtually no trees or shrubs, and the vegetation consists largely of terms, grasses and sedges. This is the wettest zone, specially during the garua seazon, receiving as much as 2.5 m of rain in some years.

Brown Zone: It is intermediate between the dense Scalesia forest and the Miconia shrubb vegetation. It is an open forest dominated by cat’s law, tournefortia pubescens, and aunistus ellipticus. Trees are heavily drapped with epiphytes, mosses, livertorts and ferms, which give this zone a brown appearance during the dry season. This zone has disappeared because of colonization by man.

Scalesia Zone: The transition zone merges into the evergreen scalesia forest, which is lush cloud forest, dominated by scalesia pedunculata trees. This type of forest occurs only on the higher islands and, being the richest zone in terms of soil fertility and productivity, has been extensively cut down for agricultural and cattle ranching purposes. The scalesia forest is diverse and has many edemic species.

Transition Zone: It is intermediate in character between the scalesia and arid zones, but dominated by different species than either of the adjacent zones. The forest is still mainly deciduous. It is much more dense and diverse than forest of the arid zones and it is often difficult to say whether any species is dominant.

Arid Zone: Is the most extensive vegetation zone. It is a semi-desert forest dominated by deciduous trees and shrubs. The plants have adaptations to withstand drought. There are great numbers of endemic species. Lichens are abundant in this zone because they are tolerant of dry conditions and are capable of absorbing moisture from the occasional garua mist.

Miconia Zone: The southern slopes of San Cristobal and Santa Cruz are the only places where there is a dense shrubby belt of Miconia Robinsoniana. Native trees are absent from this zone and ferms are abundant in the herb layer. There are also many liverworts than elsewhere.

Coastal Zone: This evergreen zone is based on salt tolerance abilities of certain species at the land/sea interface. The type of vegetation found varies greatly. The mangroves form forest in coves, while on beaches there are vines, grasses and shrubs. Many plants in this zone are adapted dispersal by the sea and few are endemic because of the unstable nature of the environmental and high immigration rates.