The Galapagos Islands. The name conjures up images of rare birds, giant tortoises and fearless sea lions, but there is another side to this archipelago. A side may appeal to a geologist more than an ornithologist or herpetologist, because the Galapagos are a classic example of a geologic hot spot.
Sally Lightfoot (grapsus grapsus) crabs crawl across jet black lava on the island of Santa Cruz.
A hot spot is where volcanic islands are formed as a plate of the Earth’s crust slowly moves over a stationary magma source. The molten rock is brought to the surface by what is known as a mantle plume, because it is thought to be rising directly from deep within the mantle. The result is a chain of islands that follows the direction of the plate’s movement. The further from the hot spot, the older the islands are, until they ultimately erode away into the ocean.
The Hawaiian Islands are the best known example of this phenomenon, but many other spots exist, some of which are not under water. Yellowstone is a prime example of a hot spot on land. While the Galapagos are similar to these other spots, they are unique in that the hot spot occurs at a point between two of the Earth’s plates, the Nazca Plate, moving to the east-southeast, and the Cocos Plate which moves northeast. This has caused islands to form in two directions instead of the straight line chain we see with Hawaii. The geology is further complicated by the Galapagos Spreading Center between these plates.
Prince Phillip’s Steps, a narrow path in a fissure of the
volcanic ridge that forms Genovesa Island.
With The Galapagos being so active — the latest eruption was in 2009 –the landscape could serve as a textbook for identifying volcanic features.
Our introduction to these geologic examples came at Genovesa Island, one of the oldest islands, which is the rim of a giant, ancient caldera poking above the surface of the sea. The captain sailed our boat, Yolita II, through the eroded opening in the crater and into the middle of the volcano. From our anchorage the shape was unmistakable.
Darwin’s Bay on Genovesa Island. The island is one big crescent-shaped bay formed by the remnants of a large volcanic caldera.
As we moved southwest, toward the hot spot and the younger islands, we came to Bartolomé Island. Here formations such as Pinnacle Rock, known as “The Guardian of the Isles,” and a small submerged caldera that looks like a moon crater just off the coast, are obvious calling cards of more recent volcanic activity.
Pinnacle Rock, just off the coast of Bartolomé Island.
As we hiked to the top we found that much of the island’s topography looked otherworldly, with lava bombs and flows limiting the vegetation, and spatter cones leaving craters from slightly more explosive eruptions.
A Lava Lizard, one of the few creatures willing to call forboding Bartolomé Island home.
Pinnacle Rock takes on a gravity-defying angle from Santiago
Just across a narrow channel, on the nearby island of Santiago, we found another barren landscape created by a very young, black basalt lava flow. Young in this case meaning about 130 years, which may sound slightly older than young, but geologically speaking that is just the blink of an eye. We were obviously getting very close to the hot spot itself.
The molten rock that formed this new piece of land when it flowed into the sea a century ago left numerous types of mind-boggling patterns and designs. The differences in the ridges, waves, and bubbles are caused by varying speeds in the cooling process.
The tropical sun on the black basalt flow takes a toll on Veronica.
Somehow, miraculously, life always finds a way.
Our next destination, the island of Isabela, is the largest of the Galapagos. Here the tops of the volcanos rise over a mile high above the sea. From our beginning at sea level on our boat we took a bus several miles inland, through dense jungle, up the slopes of Volcán Sierra Negra.
When the road ended we hiked about two miles to the rim of the active volcano, above the clouds. From that vantage point we could look down on the floor of the caldera which is covered with black, freshly hardened lava from the last eruption in 2005. That crust is still hot, warmed by the massive magma chamber lying just below the surface.
To the north of the Sierra Negra Volcano, on the west coast of Isabela, we stopped off to check out the formations at Tagus Cove. By boarding small inflatable dinghies we could get up close views of tuff cliffs along the shore. Tuff is a sedimentary form of volcanic rock that forms when ash is piled up in layers over the ages and compressed into soft stone. Because of its softness, tuff easily erodes into interesting and unique formations.
The various types of volcanic rock have also led to a peculiar situation where the beaches on the islands can range in color from black to white. The crushed basalt of the lava flows makes for black sand, while the tuff creates deep reds and browns, and the classic white sand that comes from crushed coral and shells can be found throughout the islands.
We were now nearly on top of the hot spot. Right next to Isabela is Fernandina Island, the youngest and most recently active of all of The Galapagos. We dropped anchor and made our way ashore at Punta Espinoza. While the extraordinary barren landscape of this newborn land would be expected to be the main attraction, it was overshadowed once we noticed the lava was alive.
Thousands upon thousands of endemic marine iguanas have made their home here. They have adapted to this harsh and lifeless environment by taking on the exact coloring of the lava and learning to go into the sea to find food.
They are the only iguanas on Earth that go under water, and that trait helped us spot them. They have a habit of sneezing out the salt from the seawater as they warm themselves and dry off in the tropical sun. The sound, movement, and dried up, white salt residue tended to give away their otherwise nearly perfect camouflage.
Having been to the source of these wondrous islands, the time had come to make our way back to the mainland, but not without one final example of classic volcanic landscaping. Just before we reached Baltra Island and the airport, the captain took us on a quick circumnavigation of Daphne Major. This perfect cone rising out of the sea has the quintessential volcano shape.
It really does look as if it should be in a geology textbook.
See the incredible work done at Giant Tortoise Breeding Center
Cavort with Sea Lions!
The Birds of The Galapagos – wild!
The Underwater World of The Galapagos
Our tips for visiting The Galapagos Islands – including what to pack
David & Veronica, GypsyNester.com