Soil formation of the Galápagos Islands

The Galápagos Islands are a UNESCO World Heritage site. They are an archipelago of nineteen islands in the eastern Pacific Ocean and are part of Ecuador. The Galápagos are known for theie extreme isolation and unusual animal life, with rare species inhabiting the islands.

The soils of the remote Galápagos Islands were not well studied, but a group of soil scientists began looking in earnest at the island soils in 2016. There was an expedition for a Galápagos soil survey and sample collection conducted by Belgian scientists in 1962, which was helpful in the more current research. The findings of the current study were published in the Soil Science Society of America Journal in 2021.

bird's eye view of Galápagos Islands with clouds and water surrounding islands
The Galápagos Islands are a chain of islands, or archipelago, in the eastern Pacific Islands. On the trade winds side of the island, soils are better suited to plant life as can be seen on the right hand side of each island or mountain range. This is due to rainfall and humidity in these regions. Credit: Creative Commons ISS-38

Like Hawaii, the Galápagos Islands were formed from a volcanic hotspot. However, the Galápagos have an overall drier climate than Hawaii, which influences soil formation. They also have a lower amount of dust settling from Asia. These influences result in different soil types and mineral composition on the Galápagos.

The climate of the Galápagos Islands is not typically tropical for their equatorial location – they are actually cool and dry. The islands experience cold ocean currents and prevailing south-east trade winds. As a result, the Galápagos Islands experience two main seasons: a hot season from January to May and a cool season from June to December.

During the hot season, there is a pronounced moisture gradient from low to high altitudes. This is due to wind currents and location of mountain ranges that hold humid air – and result in humidity and rainfall at higher elevations. The leeward side (opposite of the trade winds) have uniformly drier soils.

Galápagos Island terrain including hills, water, plants, beaches and soil
The Galápagos Islands are a UNESCO heritage site and valued for its unique flora and fauna. Humidity varies over the islands depending on orientation to the trade winds as well as altitude. This factor has influenced soil formation on the volcanic parent material. Credit: UNESCO

Water, in the form of humidity or rainfall, is an important part of the weathering process that creates soil. Rainfall can physically break down rock into minerals. Moisture allows soil microbes to process minerals – as part of their “diets” – which is part of the process that creates organic matter. With enough physical, chemical, and biological weathering, soil formation takes place.

Thus, the higher elevations of the Galápagos typically have more established soils. On the windward slope of the island, the weathering degree of the soils increased with altitude. This corresponded to a moisture gradient from the arid lowlands to the humid highlands.

There were soils of different ages found in various locations of the islands. How does this happen? Soil formation is a continuous process. As a soil ages, it gradually starts to look different from its parent material. That’s because soil is dynamic. Its components—minerals, water, air, organic matter, and organisms—constantly change. Some components are added. Some are lost. Some move from place to place within the soil. And some components are transformed into others.

lush plants and shrubs on hilly terrain on Galápagos Island
Soil formation on the Galápagos Islands is not uniform because of different weather like rain and temperature, as well as other factors. But some soils support microbial, plant and animal life. Credit: Igor Starukha

The Galápagos Islands’ parent materials are volcanic in nature. And the soil-forming factors of Climate, Organisms, Relief, Topography (landscape) and Parent material are all quite different on the islands than they are in, say, the United States Midwest. Areas of the island that are drier can have less mature soil than the higher, humid regions.

According to the paper’s authors “The Galápagos Islands are an ideal outdoor laboratory for studying weathering and soil formation under relatively pristine conditions. The observed soil changes in response to climate and duration of weathering have important bearings on the soils’ functioning.” This includes factors for how the soils retain and release nutrients to plant life. This could affect the evolution of plant and animal species on this unique archipelago.

Blog compiled by Susan V. Fisk from the paper published in Soil Science Society of America Journal.

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