Volcanoes of the Galapagos
The Galapagos Islands are very young in geologic terms, Espaņola the oldest of the
islands was formed 3 to 5 million years ago from a volcanic hot spot
located on the sea floor. The hot spot is an area where the magma is so hot
it burns through the earth's crust and the magma below is allowed to reach the crusts
surface forming a volcano.
As the hot spot discharges materials it begins accumulating, spreading and
rising. The discharged materials reach a level of 6,000 to 10,000 ft (2,000 to
3,000 m) from the ocean floor. As the Plate at the ocean floor moves at a
rate of 3 inches per year (5 cm) the volcano breaks free of the stationary hot spot
forming an independent island. As the hot spot continues to emit material a
new island is born using this process. As new islands are formed and the plate
continues to move a chain of islands is formed. The Galapagos hot spot is located to the
east of Fernandina, the youngest of the islands at approximately 1 million years of age.
A study of geology in action, the
Galapagos Islands is one of the world’s most active volcanic areas, with more than 50
eruptions in the past 200 years. Six of the volcanoes are still active (1 on
Fernandina and 5 on Isabela). The most recent explosion was in of 2005.
Shield Volcanoes
The type of volcanic make up characterizes the island's look. Most of
the Galapagos Islands were made from a single volcanic cone creating a high point of the
island with gentle slopes and a flat coastline. Espaņola (the oldest of the chain)
and Fernandina (the youngest in the chain) with their single volcanic cone are typical of
most of the islands known as a shield volcano.
Shield volcanoes are formed from a build of fluid lava flows. As the flow emits
from the central vent it pours out in all directions creating a broad, gently sloping cone
of flat, domical shape. The profile is said to resemble a warrior's shield giving
these volcanoes their name. The volcanoes build up slowly the result of thousands
of fluid basalt lava flows. The lava cools into thin layers, which continues to
accumulate for years, eventually giving the volcano its height. Shield volcanoes
make up some of the largest volcanoes in the world including Mauna Loa in Hawaii, which
rises 28,000 feet above the ocean floor. Isabela the largest island of the Galapagos
Archipelago was created from the fusion of 6 shield volcanoes.
Other Shield Volcanoes include the Hawaiian Islands and
Iceland where Strata Volcanoes include Mt. Fuji, Japan, Mount St. Helens,
Washington and Cotopaxi, Ecuador
Volcanic Plateaus
Volcanic Plateaus formed South Plaza, Baltra, and North Seymour
Islands. Plateaus create when the eruption of basalt lava poured quickly from
fissures rather than central vents. The lava surrounds the area and with lava flow
upon lava flow, forming broad plateaus. Lava plateaus of this type are
located along the Snake
River in Idaho, and the Columbia River in Washington and Oregon. Those lava flows are
exposed and measure more than a mile in total thickness.
Lava Flows and FieldsLava flows are streams of molten rock that pour onto the
Earth's surface from an erupting vent. Both moving lava and the resulting solidified
deposit are referred to as lava flows. Lava flows come in a variety of shapes and
sizes. They are impacted by the wide range in speeds of the different lava types
(basalt, andesite, dacite, and rhyolite), the lava discharge during eruptions, and the
characteristics of the erupting vent and topography over which lava travels.
Fluid basalt flows like those in the Galapagos can extend tens of kilometers from an
erupting vent. The leading edges of basalt flows can be as fast as 6 miles (10 km) per
hour on steep slopes but they typically travel less than 1/2 mile (1 km) per hour on
gentle slopes. When basalt lava flows are confined within a channel or lava tube on a
steep slope, the main body of the flow reaches speeds more than 18 miles (30 km) per hour.
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 Lava, the material expelled from the volcanoes is present in the Galapagos
and takes a variety of forms. On Santiago it is possible to see 2 distinct
types of lava patterns.
Pahoehoe is a Hawaiian name for
basaltic lava that has a smooth, hummocky, or ropy surface. A pahoehoe flow typically
advances as a series of small lobes and toes that continually break out from a cooled
crust. The surface texture of pahoehoe flows varies widely, displaying all kinds of
bizarre shapes often referred to as lava sculpture.
`A`a (pronounced "ah-ah") is a
Hawaiian name for lava flows that have a rough rubble-like surface composed of broken lava
blocks called clinkers. The incredibly spiny surface of a solidified `a`a flow makes
walking very difficult and slow. The clinkery surface actually covers a massive dense
core, which is the most active part of the flow. As pasty lava in the core travels
down slope, the clinkers are carried along at the surface. At the leading edge of an
`a`a
flow, however, these cooled fragments tumble down the steep front and are buried by the
advancing flow. This produces a layer of lava fragments both at the bottom and top of an
`a`a flow.
Tuff Cones
Pinnacle Rock on Bartolome has become one of the most photographed sights in the
islands. The Tuff Cone is a vertical rock formation created by the
consolidation of hardened ash. During the eruption hot lava reached the sea causing an
explosion. Particles splattered down in the shape of cone often known as a Tuff Cone
or Cinder Cone.
Lava TubesExploring the Lava Tubes in the
highlands of Santa Cruz makes an interesting and eerie adventure. These giant wormholes
are caused when the exterior portion of a pahoehoe lava flow hardens while the interior
lava continues to flow. Eventually the lava flow diminishes and there is not enough lava
left to fill the hollow tube.
Calderas and Fumaroles
A caldera is a large, usually circular depression at the
summit of a volcano formed when magma is withdrawn or erupted from a shallow
underground magma reservoir. The removal of large volumes of magma may result in loss of structural
support for the overlying rock, thereby leading to collapse of the ground and formation of
a large depression. Calderas are different from craters, which are smaller, circular
depressions created primarily by explosive excavation of rock during eruptions.
Of the many specific geologic features of interest in the
Galapagos, Isabela is the only island in the chain created by the merging of 6 volcanoes.
A 3 to 4 hour hike up the island takes visitors to one of the largest calderas in
the world at 6 x 5 miles (10 x 8 km) on Sierra Negra and to see the Fumaroles or
“steam valves” being released from the active crater.
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