gEOLOGY OF THE GALáPAGOS
Article 1
The Galapagos Islands are the products of a mantle plume, which is a large column of hot (but not molten) rock that has risen up from the asthenosphere due to differences in density caused by heat. As a plume rises to the surface, the upper portion begins to melt due to decompression, and it forms a magma chamber. This magma chamber can occasionally reach the surface and cause an eruption, eventually creating a volcano. The upward motion of the Galapagos plume pushed the lithosphere upwards; this, along with magmatic thickening of the crust, created the Galapagos Platform, the shallow area in which the Galapagos Islands are situated.
Plate tectonics also play a large role in the development of the Galapagos Islands we see today. While the Nazca and Cocos plates moved, the mantle plume remained; this resulted in the creation of a chain of seamounts and islands that gets older to the south-southeast. As the plates shift and islands moved away from the mantle plume, they began to cool and contract, eventually sinking beneath the ocean. Unfortunately, the oldest Galapagos volcanoes have been subducted, but there is evidence of islands dating back at least 8 million years, and some geologists believe the mantle plume could be up to 90 million years old.
Two well-defined volcano morphologies are present in the Galapagos: shield volcanoes and calderas. Shield volcanoes have a very shallow slope, and are often very wide at the base. Calderas are a basin formed inside a volcano caused by the collapse of a magma chamber. Larger, caldera-forming volcanoes exist in the western Galapagos while smaller shield volcanoes dominate the eastern islands.
I’m very eager to see the geology of the islands in person. Although volcanism isn’t my favorite subset of geology, it’s still incredibly interesting. I’m most looking forward to seeing pahoehoe, as I find its “ropy” texture fascinating (also hoping to see ultramafic xenoliths). It will also be interesting to see in person how well the wildlife blends in with the volcanic rock.
Article 2
The presence of a mid-ocean ridge (the Galapagos Spreading Center) has complicated the model for the formation of the Galapagos Islands. The mantle plume responsible for the island chain has also affected the Galapagos Spreading Center (GSC), as evidenced by gravitational, isotopic, and geochemical abnormalities; furthermore, the GSC likely lay over the plume 5-8 million years ago. The result of all these factors is that the Galapagos is home to many differing volcanoes; they have now been divided into four sub-provinces based on age, morphology, and petrology.
One of the most interesting (now solved) geological ‘problems’ of the Galapagos is that the islands are young- the oldest exposed rocks are only ~3 million years old. Biologists, however, have discovered that land and marine iguanas diverged from a common ancestor about 10 million years ago. So what happened? This is where the concept of thermal contraction as islands move away from a mantle plume comes into play. Entirely different sets of “paleo-Galapagos Islands” have existed in the past, and life has colonized all of them as they’ve come and gone.
Humans, of course, have also colonized the islands. Due to a permanent human population nearby, the Sierra Negra volcano is one of the most accessible. Sierra Negra is extremely large, and has many unusual features such as a large coastal apron, cinder cones, a complex caldera, and a wide system of fissures. High seismic activity is also present around the caldera. The island of Santa Cruz supports a human population as well, and some of its geologic features such as scoria cones have been used as building material to support this population. Santa Cruz is also home to other interesting geologic features; the island contains the highest number of preserved lava tubes in the Galapagos.
I’m extremely excited to hike Sierra Negra- the landscape is absolutely beautiful and in some places, looks like another world entirely. The overwhelming presence of basalt is something you just can’t see in southern New Jersey. Although I’m not sure if we will be ascending any of the cinder cones, I’ve come to develop a certain respect for them after scrambling up one with the geology club in Utah. One step forward can lead you to slide 5 steps backwards, but I’m sure that the view from the top, especially in the Galapagos, is worth it.
The Galapagos Islands are the products of a mantle plume, which is a large column of hot (but not molten) rock that has risen up from the asthenosphere due to differences in density caused by heat. As a plume rises to the surface, the upper portion begins to melt due to decompression, and it forms a magma chamber. This magma chamber can occasionally reach the surface and cause an eruption, eventually creating a volcano. The upward motion of the Galapagos plume pushed the lithosphere upwards; this, along with magmatic thickening of the crust, created the Galapagos Platform, the shallow area in which the Galapagos Islands are situated.
Plate tectonics also play a large role in the development of the Galapagos Islands we see today. While the Nazca and Cocos plates moved, the mantle plume remained; this resulted in the creation of a chain of seamounts and islands that gets older to the south-southeast. As the plates shift and islands moved away from the mantle plume, they began to cool and contract, eventually sinking beneath the ocean. Unfortunately, the oldest Galapagos volcanoes have been subducted, but there is evidence of islands dating back at least 8 million years, and some geologists believe the mantle plume could be up to 90 million years old.
Two well-defined volcano morphologies are present in the Galapagos: shield volcanoes and calderas. Shield volcanoes have a very shallow slope, and are often very wide at the base. Calderas are a basin formed inside a volcano caused by the collapse of a magma chamber. Larger, caldera-forming volcanoes exist in the western Galapagos while smaller shield volcanoes dominate the eastern islands.
I’m very eager to see the geology of the islands in person. Although volcanism isn’t my favorite subset of geology, it’s still incredibly interesting. I’m most looking forward to seeing pahoehoe, as I find its “ropy” texture fascinating (also hoping to see ultramafic xenoliths). It will also be interesting to see in person how well the wildlife blends in with the volcanic rock.
Article 2
The presence of a mid-ocean ridge (the Galapagos Spreading Center) has complicated the model for the formation of the Galapagos Islands. The mantle plume responsible for the island chain has also affected the Galapagos Spreading Center (GSC), as evidenced by gravitational, isotopic, and geochemical abnormalities; furthermore, the GSC likely lay over the plume 5-8 million years ago. The result of all these factors is that the Galapagos is home to many differing volcanoes; they have now been divided into four sub-provinces based on age, morphology, and petrology.
One of the most interesting (now solved) geological ‘problems’ of the Galapagos is that the islands are young- the oldest exposed rocks are only ~3 million years old. Biologists, however, have discovered that land and marine iguanas diverged from a common ancestor about 10 million years ago. So what happened? This is where the concept of thermal contraction as islands move away from a mantle plume comes into play. Entirely different sets of “paleo-Galapagos Islands” have existed in the past, and life has colonized all of them as they’ve come and gone.
Humans, of course, have also colonized the islands. Due to a permanent human population nearby, the Sierra Negra volcano is one of the most accessible. Sierra Negra is extremely large, and has many unusual features such as a large coastal apron, cinder cones, a complex caldera, and a wide system of fissures. High seismic activity is also present around the caldera. The island of Santa Cruz supports a human population as well, and some of its geologic features such as scoria cones have been used as building material to support this population. Santa Cruz is also home to other interesting geologic features; the island contains the highest number of preserved lava tubes in the Galapagos.
I’m extremely excited to hike Sierra Negra- the landscape is absolutely beautiful and in some places, looks like another world entirely. The overwhelming presence of basalt is something you just can’t see in southern New Jersey. Although I’m not sure if we will be ascending any of the cinder cones, I’ve come to develop a certain respect for them after scrambling up one with the geology club in Utah. One step forward can lead you to slide 5 steps backwards, but I’m sure that the view from the top, especially in the Galapagos, is worth it.