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Roger Weller, geology instructor

Galapagos Islands
by Joanne Soper
Physical Geology
Fall 2011    


                                                 The Galápagos Islands


In total, there are sixty-one islands and islets that make up the Galápagos Islands. There are thirteen
major islands, in alphabetical order: Baltra, Espanola, Fernandina, Floreana, Genovesa, Isabela, Marchena, Pinta,
Pinzon, San Cristobal, Santa Cruz, Santa Fe, and Santiago. They are a part of the South American country of
Ecuador. They are approximately 600 miles (1000 kilometers) to the west of Ecuador in the Pacific Ocean on the
 Equator, between 1.5° north and 0.5° south, and 89° to 92° west. The ocean surrounding the islands and 90% of

the land surface are designated as natural sanctuary or national park areas.



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     These islands are young according to geological times; they were formed between three and ten
million years ago in a hot spot in the Earth’s crust. Three tectonic plates meet here, the Pacific, Cocos, and
Nazca. Volcanic eruptions in the ocean added layer upon layer and pushed upwards - the islands were born.
The tectonic plate movement shifts the islands to the east at the rate of about five centimeters a year.
Fernandina and Isabela (the largest), are the two westernmost islands. They are the youngest and most active
islands today.

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Erosional remnant of a lava flow

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Small shield volcano


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 Prominent shield volcano                        


See where the lava flowed downward


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Shield volcano – many lava flow layers

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     Waste action cutting away base


There are several other islands in the Galápagos that have volcanic activity. Isabela has the tallest volcano, Wolf
Volcano, which is 5600 feet high (1707 meters). The islands are shield volcanoes. According to Weller’s definition,
 a shield volcano “is a large basaltic volcano that is very wide but has a low profile. This type of volcano is so
named because it resembles a Roman shield laid flat on the ground.” Interestingly, Isabela is a combination of
six volcanoes. The lava flows filled in the spaces between the volcanoes to form a single island.


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Did a tsunami bring sand & kill trees?

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   Layers of lava flow above pool


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Erosional remnant – “Sea Stack” 


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               Layers of thin lava flows


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Collapsed magma chamber

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Europeans first came to the islands in 1535. Father Tomás de Berlanga, a Spanish priest and Bishop of
Panama, recorded the first visit. In 1835 Charles Darwin visited the islands on the MHS Beagle. As the naturalist
onboard the ship, Darwin collected samples and made notes of the things he found on the islands. After he
returned home, he looked over the finch specimens and the limited notations that he made concerning them,
and had his first thoughts about the theory of the natural selection. Ecuador declared in 1959 that the
uninhabited areas of the islands were national park land.  In 1978 UNESCO named the Galápagos the first World
Heritage site.


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Soil production – breakdown of rocks and plants 

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                         Darwin’s finch



Today, Santa Cruz, San Cristóbal, Floreana, Isabela, and  Baltra are the five islands that are inhabited.
Santa Cruz and San Cristóbal have the largest areas of human population.


Galápagos tortoises, Galápagos marine iguanas, and blue-footed boobies are the most popular wildlife
to see. It is believed that all of the plant and animal species floated or were blown to the islands.


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Pelican and crab on rounded stacked boulders that show evidence of powerful storms

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      Galápagos fur sea lions - smallest in the world


The tortoises have a shell about four feet (1.2 meters) long and can weigh as much as 595 pounds (270
kilograms).  When sea traffic along the area became more popular, ships used the islands for a port of call and
loaded the giant tortoises onboard for food.  Flipped onto their backs, the tortoises could live for weeks
without any food or water and provided easy fresh meat for sailors.  Of the Pinta Island tortoises, only Lonesome
George remains alive today.  At approximately ninety years old, breeding him with other female tortoises has, so
far, not produced any hatchlings.


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                                     Galápagos tortoise

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                  Male tortoises argue over females


The endemic (found only here) Galápagos marine iguana is the only lizard that swims in the ocean.
It feeds on the algae and basks in the sun on the lava rocks on shore digesting its food. While underwater,
it has taken in a lot of salt, so it sprays salt water out of an opening on its head, with much of the salt
remaining dried on its head.


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                           Iguana on sand – broken down basalt

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                              Dried salt on iguana head


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                   Iguana and crabs on water-worn vesicular basalt 

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                   Iquana basking and digesting algae



The blue-footed booby is a bird, about thirty-two inches long, with noticeable turquoise colored
webbed feet.  Their name comes from the Spanish word “bobo,” meaning clown or clumsy.  The birds are
awkward moving on land and during mating times the males lift their feet in dance-like motions in hopes
of attracting females.  Because of their protected status, most of the wildlife on the islands did not learn to
fear humans, so they remain in the open for viewing when approached.


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    Blue-footed booby & nitrate deposits (polite term for bird droppings)      


Tourism to the islands is limited. Starting in 2007, tourists were required to buy a transit card. Anyone
wishing to remain on the islands for work or other personal reasons, must also buy a special card. The purpose
of the card is to have better control of the islands, its visitors, and migration. All tourists who visit the National
Park areas must be accompanied by a certified Galápagos National Park guide at all times. Great care is taken to
preserve the unique and fragile environment. While on the airplane from Quito, Ecuador to the airstrip in the
Galápagos, even the overhead luggage bins are sprayed with a disinfectant/insecticide to take care not to
introduce any foreign organisms to the islands. No smoking or fires of any kind are allowed in any of the national
park areas.


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Low profile shield volcano  


All photos taken by Joanne and Paul Soper, May 2010

Information taken from the Galápagos Islands Web site, brochures, and guide lecture information.

Darwin and finch information taken from Beak of the Finch, by Jonathan Weiner.