This past week, I have been sharing with you our discoveries while we were in the Galápagos in a series titled, The Islands of the Galápagos. The strange beauty and attraction of these volcanic upwellings wove their mystery around us just as they have others who have visited since the archipelago was first discovered in 1525 by the Bishop of Panama, Tomas de Berlanga.
Today, I would like to expand upon the geology and geography of the Galápagos archipelago and share with you some of the resources that aided in our understanding of these enchanted islands.
The Galápagos archipelago consists of 18 main islands, 3 smaller islands, and 107 rocks and islets. The islands are located at the Galapagos Triple Junction – a confluence of three tectonic plates, the Cocos Plate, the Nazca Plate (which is moving east/southeast), and the South American Plate. It is also atop the Galapagos hotspot, a place where the Earth’s crust is being melted from below by a mantle plume, creating volcanoes.
Geology of the Galápagos
Geology (from the Greek γῆ, gē, i.e. “earth” and -λoγία, -logia, i.e. “study of, discourse”) is a field of science comprising the study of solid Earth, the rocks of which it is composed, and the processes by which they change.
Using our North Star Geography program as our guide, we learned about plate tectonics prior to our departure. There are three types of boundaries between tectonic plates:
- Divergent Boundaries – where two plates are moving away from each other
- Convergent Boundaries – where two plates push up against one another
- Transform Boundaries – where two plates move horizontally, slipping past each other in opposite directions
After reading the chapter, we created edible models of the boundary types in STEM Club (see my earlier post, Plate Tectonics, for lesson details). This was a great activity and the kids really enjoyed manipulating the earth’s plates (i.e. graham crackers).
Dynamic Plate Boundaries
The lithosphere is broken up into 15 major plates, which move with respect to one and other. Mid-oceans ridges, a type of divergent boundary, are located at the edges of plates moving away from one and other on the ocean floor. One such mid-ocean ridge, the Galápagos Spreading Center, is located just north of the archipelago.
Mid-ocean ridges are often offset by fracture zones or transform faults. A major transform fault is located just north of the islands.
Subduction zones occur where plates collide. A major subduction zone is located where the Nazca and Cocos Plates are subducting beneath the South American and Carribean plates. Subduction zones are marked by deep trenches and overlying chains of volcanoes (the Andes, for example).
The Galápagos Islands are one of most active oceanic volcano areas in the world. Like many oceanic islands, the Galapagos are thought to be the product of a mantle plume – columns of hot rock that rise from deep within the Earth. These plumes rise because they are hotter and therefore less dense, than the surrounding rock.
As a lithospheric plate moves over a mantle plume, a chain of volcanoes is created. The volcanoes get older in the direction of plate motion. The Galápagos Islands are located on the Nazca Plate, which is moving east-southeast. Thus, the islands get older to the south-southeast and it has produced a chain of seamounts known as the Carnegie Ridge.
A second seamount chain, the Cocos Ridge, extends northeast from the Galápagos Spreading Center. Thus a chain of volcanos was produced on both the Cocos and Nazca plates.
Geography of the Galápagos
Geography (from Greek γεωγραφία, geographia, lit. “earth description”) is a field of science dedicated to the study of the lands, the features, the inhabitants, and the phenomena of the Earth.
In our North Star Geography text, we also learned that there are a number of different kinds of volcanoes. We observed two distinct types of volcanoes in the Galapagos. In the west, on the islands of Isabela and Fernandina, large volcanoes with an “inverted soup-bowl” morphology and deep calderas occur. In the east, smaller shield volcanos with gentler slopes occur.
One of the activities suggested in the North Star Geography activity guide, is to make a topographical salt dough or cookie dough map. The Galápagos islands were the perfect “model” for this activity.
In addition to the salt dough map, the kids enjoyed creating an accordion-style picture dictionary as we were traveling. You can download this free printable, Geography Picture Dictionary, for your personal use. It is a great supplement for North Star Geography. Children can sketch the geography specific to a region (as we did) or use it in a more general sense.
Craters & Sink Holes
The twin craters of Los Gemelos (one of which is pictured above) are a highlight of the Santa Cruz highlands. Though a lesser know attraction, Los Gemelos, are actually sink holes, not volcanic craters, on the highest part of Santa Cruz. These depressions were formed by collapsing underground lava tunnels.
This region also boasts of a beautiful Scalasia forest with trees covered by many epiphytes. In recent years, however, some plants have been introduced that are invading the Scalesia pedunculata forest rapidly. What was interesting here was that in addition to the Scalasia, cacti were also present (though more abundant in the lowlands).
In contrast to the dry coastal lowlands, the highlands are covered by mist in the garua (foggy) season and receive thus much more moisture and support a more luxuriant vegetation.
If you would like to further explore the Galápagos from the comfort of your home or if you are planning to visit yourself, my multidisciplinary unit study, Galápagos Across the Curriculum, provides ample opportunity for kids to explore the diversity and remarkable history of the islands through a variety of hands-on science activities and projects.