Galapagos Island Geography and Geology - Part Three - Ocean Currents

San Cristobal Island

This is the final of a three-part series of articles in which I discuss the geology of the Galapagos Islands. In Part One I talked about the tectonic plates that lie beneath the sea and under the land and explained that without the constant movement of the tectonic plates, their crashing into one another, forcing the hot magma to break through the Earth's surface (called the lithosphere), there would be no Galapagos Islands at all. Part Two focused on the actual formation of the islands from volcanic action that occurs when those tectonic plates collide. Each and every one of the Galapagos Islands, their topography, the sheer cliffs that you see and that have become the nesting sites for bird and animal life found no where else on earth, the beautiful outcroppings, marine life, SCUBA sites, black sand beaches, crystalline beaches - all resulted from volcanic activity. Here, in Part Three, I will talk about the Pacific Ocean currents, particularly how the hot and cold currents impact and define the plant, animal, bird and marine life throughout the Galapagos Islands.

It's very important that you know that it is a very personal journey I take with you in these pages. These enchanted islands have been my home and that of my family for three generations. They are, to me, a constant source of joy, mystery and delight. From childhood, I recognized that I lived in a wondrous and unique place. I am commited to imparting my knowledge and deep concern for the environment to my guests and, through this blog, have a chance to share my experiences with you. Come and share the world I love with me. For now, experience just a little of what the Galapagos Islands have to offer in this video from my good friend Alex at Aqua Surround.




The Galapagos Islands is, in so many respects, a study in contradictions and diversity. I tell all of my guests, "Expect the Unexpected."

Cactus on Santa Fe Island

Tourists to the Galapagos Islands generally arrive knowing we are located on the Equator and expecting seething heat and unmitigated sunshine. I’m happy to tell you – like just about everything else here – the weather will surprise you. It is hot here, but usually not excessively so. We have months of daily rain showers, but only brief ones. We have periods of mist. We have water cold enough that you’re more comfortable in a wet suit, even snorkeling in the middle of the day during our hottest months. We have cactus, sheer bare cliffs and rock and lava-encrusted surface area, but we also have a few fresh water lakes and lagoons populated with flamingos. We are situated directly on the Equator, but we have penguins. All of these apparently anomalous conditions are due to the ocean currents as they affect the climate, habitats, ecology, marine creatures and animal life of the Archipelago.

Charles Darwin himself noted his surprise at the moderate climate relative to the fact that the islands are situated on the Equator. He wrote,  “[It] is far from being excessively hot…excepting during one short season, very little rain falls, and even then it is irregular.” He went on to explain why, stating, “[T]his seems chiefly caused by the singularly low temperature of the surrounding water, brought here by the great southern Polar Current.” As proved to be true about many things, Darwin was right.





Think of currents as rivers flowing in different directions and intersecting within the Pacific Ocean, as shown in this diagram:

Ocean Currents Map from The National Weather Service
http://www.srh.noaa.gov/jetstream//tropics/itcz.ht

Five ocean currents intersect at the location of the Galapagos Islands and have a profound impact on its  climate and, accordingly, its flora, fauna, land, sea and bird life. The prevailing currents are Cromwell, Peruvian, Humboldt, and the Panama Current. The fifth current, El Niño, sometimes has a devastating effect as well. The weather at any given time is informed by and determined on the basis of the prevailing current. We even have seasonal climate changes here – all brought about by the ocean currents. The mix of these currents and the related location of each island causes a wide variation of water temperatures from month to month and island to island.

Humboldt Current

Galapagos Penguins Swimming in the Humboldt Current
Photograph from Creative Commons by Lebatihem

Darwin, referring in the above-quote to the "Polar Current" was referring to the Humboldt Current (also called the Peru Coastal Current). It is cold because it begins its route in the frozen ice of Antarctica, then travels up the western coast of South America before reaching the Galapagos Islands. To be sure, in its travels, the current loses its frozen aspect, but still it remains a cold ocean current. It has the energy and means to cool the land and sea temperatures, thus giving the Galapagos Islands something other than the over-heated humid tropical climate you might expect. Because of the effect of the Humboldt Current, our climate is actually subtropical. It is because of the Humboldt and Cromwell Currents that Penguins thrive in an equatorial environment. Read more about this stunning phenomenon in my post, Galapagos Penguins - Yes, Penguins on the Equator.

Fur Seal
Photograph from Creative Commons by A. Davey

Not only Galapagos Penguins, but also Galapagos Fur Seals immigrated to the Galapagos Islands, and evolved and adapted to this climate, by way of the Humboldt Current.

Typical Cloud Covering on Santa Fe Island

Winds accompany the Humboldt Current and, together, the water temperature and wind form a low-lying layer of clouds which often are visible over the islands. This makes for pleasant temperatures.

Rabida Island Enveloped with Guara
Photograph by David Tana at superoceras.blogspot.com

The clouds, in turn, sometimes envelop the highlands throughout the archipelago in a persistent light mist known as garúa. You might have read that we have a dry season in the summer and fall, but this is actually a misnomer. It is called the dry season not because it is actually dry, but because the persistent garúa made it difficult for settlers to collect drinking water.

Throughout the Islands we feel the impact of the Humboldt Current predominantly during the summer and fall, and strongest of all in the month of September.  This is the choppiest time of year to be on a boat in the Galapagos Islands. 

Cromwell Current

Underwater Footage
Showing Variety of Marine Life
Made Possible by the Ocean Currents
All Underwater Photos by Brian Postill

The other cold water current is the Cromwell Current, also known as the subequatorial Countercurrent. It originates in the depths of the western Pacific Ocean and flows eastward. At the Equator, the Humboldt turns west, assisted by the Earth's rotation and seasonal winds, and joins with the Cromwell before heading straight toward the Galapagos. Together, they slam into the islands, pushing deep cool water to the surface. The deep water has an abundance of accumulated nutrients. As they emerge from the depths to the surface, the nourishing phytoplankton form the bottom rung on the ocean's food chain.


The Cromwell is huge, extending the entire length of the equator in the Pacific Ocean. This enormous submarine river current is 250 miles wide, 3500 miles long and is 1000 times the volume of the Mississippi River. The surface currents of the Pacific Ocean flow eastwardly.

Galapagos Penguin
Photograph from Creative Commons by Hanumann

The Galapagos Penguins also rely on this ocean current as it brings nutrient-rich fish on which the penguins feed. During the day, the Penguins use the Cromwell Current's cold waters to keep themselves cool.

The very cold Cromwell Current (just 13 degrees Celsius at its core) lies 300 feet underneath the surface current and is like a river flowing in the opposite direction. Because it is so high in nutrients and oxygen, the Cromwell Current supports a wide array of marine life. It is unusual for the Cromwell current to appear in the eastern Galapagos Islands. For the most part, it surfaces near the western islands of Fernandina and Isabela. Then, upon encountering the submarine Galapagos platform it dissipates toward the center of the archipelago.

The Cromwell Current has a dramatic impact on the marine environment throughout the Galapagos Islands.

Recently a blogger wrote about his diving experiencing around Isabela Island in the Cromwell Current, where the water temperature is about 58 degrees F (16C). He identified varied and fascinating marine life that might be encountered in this nutrient rich environment: "Mola Mola that were very close to us ... seahorses everywhere, bull sharks, red-lipped bat fish, sea lions, flightless cormorant, schools of salemas, dozens of sea turtle, king angel fish, Mexican hog fish, harlequin wrasse, pompanos, and bonitos ... big marine iguanas eating under the water.  After one of our dives we did a panga ride along the cliff where we spied penguins, flightless cormorants, marine iguanas relaxing, hunting and swimming, sea lions, pelicans, and resident blue footed boobies." More from this blog.

Panama Current

The Panama Current is a warm water current that predominates from about November (the beginning of what we call the "wet" season) until May. The water temperature rises, the skies clear with the exception of occasional rain showers. The water during the period of the Panama Current is actually clearer because there are fewer nutrients concentrated in it. The marine life is very rich during this period as well. The warm water brings loads of schools of fish as well as sharks and rays.

El Nino

School of Galapagos Island Fish Before El Nino
Photograph from Sciencewithoutborders.org

Every 2 to 7 years the strong westward-blowing trade winds subside. Instead of allowing the Humboldt Current, so rich in nutrients, to come in to feed and nourish the aquatic life and the animals and birds that depend on that marine life for survival, the warm waters stagnate around the Galapagos archipelago. The aquatic life typical to the Galapagos Islands is unable to survive in the absence of cool water rich with nutrients. So, the fish leave the archipelago in search of cooler waters in which to thrive. The result can be devastation as the marine and animal life that depend on the schools of fish is left without a food source.

Iguanas Shrink in both weight and height without nutrition
Photograph from Sciencewithoutborders.org

In essence, El Nino breaks the delicate balance of nature that feeds the fish, birds and marine animals such as the Galapagos Penquins, Bobbies, Flightless cormorants and Marine Iguanas. And when the feed cycle is broken, so is the breeding cycle. The long-term impact on the fish, birds and marine animals that depend on those fish for survival is challenged. Tortoise species have died because of El Nino. Land iguanas shrink in both height and weight when forced to live without sufficient nutrition during a period like El Nino. Read more about this occurrence in my Iguana blog post.


NASA has extensively studied the effects of El Nino on the Galapagos Islands. From a satellite, it photographed the amounts of chlorophyll in the water during and after El Nino. These satellite maps show chlorophyll concentration (which corresponds with the density of microscopic ocean plants, called phytoplankton) during El Niño (top) and La Niña (lower). Blue represents low concentrations, while yellow, orange and red indicate high concentrations. Currents that normally fertilize the phytoplankton reverse during El Niño, resulting in barren oceans. These same currents are strengthened by La Niña resulting in an explosion of ocean life. It doesn't take much to imagine that in periods of El Nino, when there is nothing left for the fish to eat, the fish must abandon the Galapagos for better feeding grounds, leaving the animal life that depends on them to seek alternatives and, sometimes, to become extinct.

The images from 1998 graphically show that the unique Galapagos ecosystem was severely affected and many species, including sea lions, seabirds, and barracudas, suffered a very high mortality level. However, during the second week of May, 1998, the ocean temperatures plummeted 10 degrees in one day, and the ocean productivity exploded with large phytoplankton blooms. Rapidly, many species recovered and the land species started to reproduce. Read more from NASA about the El Nino effect and the importance of the underwater plant life. There are photographs of the devastation that El Nino had on marine life, including sea lions and iguanas. During a period of El Nino the Galapagos National Park Service is diligent in following and studying all the animal, bird and marine life and providing human support to forestall harm to any species.

Green Surface During El Nino
Photograph from National Oceanic
and Atmospheric Assn. U.S. Gov.

On the positive side El Nino does bring rain and favors vegetation growth. The Galapagos Islands see spectacular flowering cactus and much greener landscapes during El Nino than at other times. And, surely, El Nino is part of the circle of life and the environmental eco-system that made the Galapagos Islands what they are today.











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