Guest post for VolcanoCafé by René Goad
First of all I would like to thank Carl Rehnberg for inviting me to write a guest post and I will be talking a bit about the Galapagos Islands.
For a good few years I’ve been wanting to visit the Galapagos Islands with the Sierra Negra Volcano and the unique wildlife being the main draw to it. In March 2016, I finally got my chance and it didn’t disappoint either. I got to see some fascinating hotspot volcanism as well as some unique animals such as the Green Turtle, the Galapagos Giant Tortoise, the Marine Iguana, the Blue Footed Booby, and many more.
So, we’ll begin with a brief background of the Galapagos Islands. The archipelago is located 563 miles west offshore of Ecuador and the largest islands are San Cristobal, Santa Cruz, Santiago, Isabela, and Fernandina. The Galapagos sits atop a volcanic hotspot in the Pacific Ocean which formed the islands. Historical eruptions had occurred on the islands of Santiago, Marchena, Pinta, Isabela, and Fernandina, but the most volcanically active part of the Galapagos tends to be on the western islands of Isabela and Fernandina.
On the Bartolome Island day trip one may observe plenty of volcanism all around. At about an hour into the boat journey one may get a good perspective of the Santa Cruz shield volcano complex before passing by Daphne Major Island, a tuff cone which hosts a colony of birds. As one gets progressively closer to Sullivan Bay, Santiago Island volcanism becomes more evident. The shield volcanoes, the Pahoehoe lava fields, the parasitic cones, the basalt rocks, and Bartolome Island itself.
In Sullivan Bay I snorkelled with a life jacket on alongside the lava shoreline, I looked into the sea with a mask on and noticed that the solidified lava flows dipped vertically onto the sea bed. I could imagine that the lava flows went through the same process as with what we currently see on the east coast of Big Island, Hawaii from the lava flows of Kilauea. Sullivan Bay was also the area where I had the pleasure of spotting a Green Turtle in the sea and two Galapagos Penguins on the lava shoreline.
Upon reaching the beach at Sullivan Bay I went to checkout the solidified lava flows which were black in colour and had a ropey texture, yep this was definitely lava of the Pahoehoe type. These lavas were most likely to have come from the 1897 eruption. Three historical eruptions are known to have occurred on Santiago, the first one being roughly in 1759 which occurred at James Bay on the west side of the island.
Although the James Bay eruption hasn’t been known to be historically observed, it was confirmed because Charles Darwin had discovered fragments of marmalade pots (left behind by buccaneers) embedded in lava flows. The next two eruptions occurred in 1897 and in 1904-1906 on a small shield volcano at the southeast end of the island, this is where I believe the source of the Sullivan Bay lava flows came from. Just across the water is Bartolome Island, which is mainly built up of an extinct volcanic cone but has a western peninsula containing eroded tuff cones. Perhaps the most prominent feature of the western end of the island is Pinnacle Rock, a remnant of an eroded tuff cone.
Come ashore on the island and one may observe a variety of volcanism on the way especially Pahoehoe lavas, lava channels, and spatter cones. One may also notice a variety of colours on the island such as orange, orange-brown, red, reddish-brown, brown, yellowish-green, and grey, but orange-brown is the most prominent colour here. Lava Cacti (a type of cactus) flourishes on the lava where they are embedded. Spatter cones are prominent on the east side of the island and the viewpoint at the peak offers great views of the Santiago landscape ahead as well as nearby islands especially Bainbridge Rocks and Sombrero Chino also formed as a result of volcanic eruptions.
Over to Isabela Island now, and if you look at the map of the Galapagos Islands then not only you will find that Isabela is the largest island in the archipelago but it also resembles a seahorse. This is because of the six shield volcanoes which formed over time and merged to form one island, they are: Sierra Negra, Cerro Azul, Alcedo, Darwin, Wolf, and Ecuador. Based on historical observations, historical eruptions have occurred on five out of six volcanoes on Isabela, the only one not having done so was Volcan Ecuador at the northwest tip of the island.
The only volcano on Isabela to have public access is Volcan Sierra Negra, which can be easily accessible through a day tour booked in Puerto Villamil. The rest of the volcanoes are restricted only for scientists. Beginning with the settlement of Puerto Villamil, one doesn’t have to travel far to find evidence of volcanism. Solidified lava flows are present down at the beach and vegetated lava fields can be seen just outside of town. Out in the bay are the islets of Tintoreras which are remnants of an eroded A’a lava flow and a bit further out is Tortuga Island which is an eroded tuff ring, both of which are accessible through tours although I myself didn’t go to either of them.
To Sierra Negra now, and the journey by foot begins at the park entrance where one has to walk north up the trail on the vegetated slopes before walking along the east caldera rim. It is from the east caldera rim where one gets a good view of the vast summit caldera of the Sierra Negra shield volcano. The summit caldera has a diameter of 7 x 10.5 km. Three prominent features occupy the caldera floor, the first one being the lava flows from the 2005 eruption where they accumulated along the east caldera wall, then over on the west side of the caldera there is a long ridge which runs parallel with the west caldera wall, and finally a large fumarolic area (Volcan de Azufre) is present in between the ridge and the west caldera wall. The south central part of the caldera floor has experienced an uplift.
Descending onto the northeast flanks the landscape becomes increasingly barren as the vegetation diminishes to a point where only cactuses are present on the solidified lava flows. It is within this area where one may encounter a rich variety of volcanism including lava flows (of both the Pahoehoe and A’a type), lava spatter, small lava tubes, collapsed roofs of lava tubes, fissures, cinder cones, scoria cones, spatter cones, and even the odd weak fumaroles, suggesting that this is one of the most volcanically active parts of the Sierra Negra shield volcano. Tourists are permitted to walk as far as the vent called Volcan Chico before turning around for the return leg.
Based on historical observations, six proven eruptions have occurred on Sierra Negra during the years of 1911, 1948-1949, 1953-1954, 1963, 1979-1980, and 2005. Other eruptions during the years of 1813, 1817, 1844, 1860, 1954, and 1957, although they were confirmed the volcano origin was uncertain. The most recent eruption of Sierra Negra began on 22nd October 2005 along a fracture within the inner north caldera wall and ended on 30th October 2005. The activity had consisted of lava fountains and lava flows which predominately descended into the caldera floor along the east caldera wall and to a lesser extent, descended the north flank.
Finally, we move on to Santa Cruz and no historical eruptions have been known on this vegetated shield volcano although some significant volcanism can be found here. Numerous parasitic cones are dotted around the flanks but the island’s highest point is on Cerro Crocker at 864m. One can get a good perspective of the island from a boat whether it would be during a day trip to an uninhabited island, or when travelling to/from Isabela or San Cristobal. Down at the area outside of Puerto Ayora is the volcanic fissure Las Grietas, a popular place for swimming. I haven’t been there myself but if I am correct then it was accessible only by boat then by foot. But just a bit further on it is possible to walk from Puerto Ayora to Playa Tortuga, here one may encounter some remnants of lava at the beach but not a lot.
But the most significant pieces of volcanism on Santa Cruz can be found in the highlands. First there’s the twin craters of Los Gemelos, two collapse pit craters which were formed as a result of a magma chamber collapse. Then there’s the lava tubes which are possible to walk in. The lava tubes and the Los Gemelos twin craters are easily accessible through highland tours which run from Puerto Ayora, you also get a chance to see the Galapagos Giant Tortoises at a ranch.
And that is the volcanism of the Galapagos from my perspective. If anybody is thinking of visiting the Galapagos islands and would like to see some volcanism then the best places for it is Bartolome and Isabela Island, and not forgetting the lava tubes of Santa Cruz.
Eruption of Sierra Negra 2005, Video credit: Karen Harpp – https://www.youtube.com/watch?v=W72foSDHjJg
René Goad is a philantrope who has set up monitoring of the volcanism of the South Sandwich Islands. In his own words: “Because no one else was monitoring that area I thought I would set it up plus it’s also give activity reference to scientists and volcanophiles who want to see what goes on there” He is also known as Ren Volcanoman on social media and has his own blogspot, http://southsandwichmonitoring.blogspot.se as well as website; www.volcanoplanet.co.uk which currently is in the middle of the process of moving host.