Galapagos Islands geology
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,
Santiago, Sierra Negra, and Wolf
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
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.
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.
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.
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.
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.