Understanding the creation and the earthquakes of the Galapagos Islands

Galapagos tectonics
Darwin had part of the answer on the Galapagos islands.
The answer to the origin of the Galápagos  was only available after 1958, when continental drift, or plate tectonics, was discovered.  We now understand that the surface of the earth is divided into massive tectonic plates which slowly drift across the globe.  The formation of the Galápagos is intimately tied to the history of the Nazca plate, on which they lie.

The Galápagos are located on the very northern edge of the Nazca plate, which is bounded by the Cocos (north) and the Pacific (west) plates (see map). The Nazca plate itself is currently drifting southeast, away from the Cocos plate and from the Pacific plate.  This movement of the Nazca plate relative to the Cocos plate is responsible for producing the cluster of volcanic islands we call Galápagos.

Divergent and transform boundaries in between the Cocos and Nazca plates - Graphic ; courtesy NOAA OceanExplorer

There is a large body of geophysical evidence for the existence of enormous plumes of hot mantle material that originate near the earth’s core and rise all the way to the crust. These plumes seem to be stable over many millions of years. and with time, they burn through the crust to form an underwater volcano which may eventually grow big enough to become an island.
But, because the crustal plate is in constant motion, the island will eventually move off of the hot spot. thereby making room for a second volcanic island. And a third, and a fourth…. Thus are archipelagos like the Galápagos formed.

Picture : Armand Vervaeck

In regions of extensive and repeated fissure eruptions, ridges are formed. Often these underwater ridges have substantial height (as much as 2,000 to 3,000 meters) and are considered to include the longest mountain chains in the world. As new oceanic crust forms at the ridges, older crust is progressively moved farther and farther from the ridge, creeping along at a rate of a few centimeters per year. This process is referred to as seafloor spreading. For this reason, we often refer to divergent boundaries as spreading boundaries. As the new oceanic crustal rock moves away from the heated ridge, it cools and contracts, decreasing the ridge height (i.e., increasing the water depth) of the ridge flanks.
Recently, the use of undersea submersibles has provided a window to view the mid-ocean ridges. Scientists have actually observed new ocean floor being produced as red-hot lava extrudes from active fissures, instantly “freezing,” or cooling, in the 2°C bottom water. Associated with the ridges are hydrothermal vents, where super-heated water, gases, and minerals escape from deep within the Earth.

Picture : Armand Vervaeck

Islands farthest from the hot spot are older and more eroded while islands near or on the hot spot are younger and steeper. Thus Isla San Cristóbal, the nearest to the mainland, is approximately four million years old and composed of eroded, rounded cones, while Isla Fernandina dates at less than 7000 years and is considered to be one of the most active volcanoes in the world. Recently former Galápagos islands, now submerged, have been discovered between Isla San Cristóbal and the mainland. This discovery may double the age of the islands. Indeed, several million years from now the present islands may likewise sink beneath the waves only to be replaced by a new set of Galápagos Islands. Who can imagine what course further evolution will take!?

Galapagos Earthquakes.
Although the Galapagos area is mainly a Hot Spot where the Nazca plate and the Cocos plate are pushed away from each other (divergent boundaries) , which allows molten lava to reach the earth’s surface, a small portion of the fault line is a transform fault where the 2 plates are striking along each other with regular earthquakes as a result (see graphic)

Galapagos volcanoes
Mid-ocean islands like the Galapagos are formed from basalt, the most basic of all types of lava.
Basalt has a very different chemical composition from the lavas that erupt from continental volcanoes, and is much more fluid. Consequently, as the lava flows build up to produce a volcanic cone, the island cones have a much shallower slope than those on the mainland.
These shallow-sloped volcanoes are called shield volcanoes and in the Galapagos, they are often compared to over-turned soup bowls.
Such shield volcanoes can clearly be seen in the younger western islands of Isabela and Fernandina. To the east, the volcanoes are lower and more eroded.

Galapagos volcanoes creation, erosion and constant movement - Graphic : courtesy Dr. Robert Rothman

(some text Courtesy – Dr. Robert Rothman, Professor Biological Sciences)
(Pictures and graphics : Dr. Robert Rothman, Armand Vervaeck and NOAA oceanexplorer)

In memory of the victims of August 24, 19XX – Taiwan and Peru

Provinces of the Ica region in Peru (Map)

Image via Wikipedia

M 6.8  24-08-1927   Depth 35 km   Taiwan – killing 11 people

At the time of the earthquake Taiwan was known as Formosa, a province of China. Huge damage and 11 people killied when a powerful
earthquake with a Magnitude of 6.8 struck the city of Tainan.

M 8.2  24-08-1942   Depth 35 km   Peru – killing 30 people

At 17:51 hours an earthquake struck the boundary area of the departments of Ica and Arequipa, situated between the 14° and 16°S parallels. Intensity IX MM (Modified Mercalli scale), felt in an area of some 18,000 km2, where great destruction occurred. Thirty people were killed by the collapse of dwelling houses and 25 were injured for various reasons.
It was felt with an intensity of III-IV on the same scale in an elliptical area of 408,000 km2 which took in the city of Huaraz on the north, Cerro de Pasco and Oxapampa on the NE, Cuzco on the east, and Moquegua on the south.

The effects on structures were noteworthy in the epicentral area. It is estimated that 30% of the buildings in the city of Nazca suffered total ruin. The neighboring towns of Acarí and Jacquí were reduced to rubble. The damage extended to the towns of Quicacha and Atiquipa, and was pronounced at Palpa. In the city of Caravelí only buildings of recent construction withstood the shock. The heavy cupola of the Church of the Lord of Luren, in Ica, collapsed, various slight damage was reported in the houses of that city, as in those of Pisco and Chinchas.

The Cordilleran towns of Coracora, Huancapi, and others suffered some damage. In the port of Chala the shaking reached such violence that several people were thrown to the ground when they lost their footing; a witness tells: “The houses rocked like a boat tossed by a storm.” The Hotel de Turistas in this place suffered crackings of its walls. Father to the SE the tower of the Cathedral in Arequipa leaned somewhat after the strong shaking. . According to the majority of the people, the shocked lasted more than a minute.

“In memory of” is highlighting deadly earthquakes of the past.
People have forgotten a lot of these human tragedies.
We @ Earthquake Report are hopeful that people in these countries and cities will learn from their history and will make sure that they are building Earthquake Proof houses and that they know what to do when the earth will be shaking again.

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– The titles of, and links to the in-depth articles of Earthquake-report.com
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Mexico – M 6.1 – Strong seaquake at a safe distance of Puerto Vallarta and Manzanillo

Fault zones of the Mexico August 24, 2010 earthquake - courtesy EMSC

Earthquake Report comment :
A strong shallow seaquake struck right on the fault line where the Pacific plate and the smaller Cocos plate collide.  The epicenter was though on a safe distance of almost 300 km out of the Mexican coast.
The earthquake was felt by some as a weak shaking, with of course no damage or injuries.
In this area, it is not the main fault line where today’s earthquake occurred (collision of Pacific and Cocos plate) which causes the highest risk, but the fault line closer to the coast where the Cocos plate and/or the smaller Rivera plate subducts under the North American plate (the steep sea ridge can clearly be seen on the Google satellite map and on the above fault line map). The biggest movement comes from the Cocos plate who travels at a rate of 40 mm/year under the North American plate.

On January 22, 2003 a large massive earthquake struck the coastal waters only 50 km from Manzanillo. This earthquake was also called the Colima earthquake (area name).
At least 29 people killed, 300 injured, about 10,000 homeless, 2,005 houses destroyed and 6,615 damaged. Most of the deaths and damage occurred in the Villa de Alvarez-Colima area. Extensive damage (VIII) at Colima and Tecoman.
Landslides closed a segment of the Colima-Guadalajara Highway and the port at Manzanillo.  A local tsunami of about 1 m  was recorded at Manzanillo.

Seismogram of the August 24, 2010 earthquake in the Pacific Ocean near the Mexican coast

The most deadly earthquake in the region occurred about 170 km to the south-east on September 19, 1985. This magnitude 8.0 earthquake (also called the Michoacan earthquake) killed at least 9,500 people, injured about 30,000, and left 100,000 people homeless.

Most important Earthquake Data:
Monday, August 23, 2010 at 07:12:00 PM at epicenter
Depth (Hypocenter) : 10 km
Geo-location(s) :
290 km (180 miles) SW of Puerto Vallarta, Jalisco, Mexico
315 km (195 miles) W of Manzanillo, Colima, Mexico

Links to important maps
USGS Did You Feel It Map
Google satellite map of the area showing the kind of terrain the earthquake took place
USGS Shaking map
USGS historic earthquakes map
GDACS Green Earthquake Alert (Global Disaster Alert and Coordination System)

* GDACS (Global Disaster Alert and Coordination System) provides near real-time alerts about natural disasters around the world.  GDACS is a Joint Initiative of the United Nations and the European Commission

QuakeSOS has been developed to help actively people who are caught in an earthquake + delivers "Earthquake Report" information on your iPhoneQuakeSOS is a FREE  iPhone application developed by Armand Vervaeck, the creator and main contributor to Earthquake Report.  The Application simplifies immediate group communication to friends and family members (with your exact GPS location) and is constantly feeding the users with “Earthquake Report” news. Together with your own family and friends, QuakeSOS will be your closest earthquake friend.

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