Riding the Landslide

It’s very, very difficult to find anything good to say about landslides; they are among the most dramatic and destructive erosion-related events. And yet scientists doing a study in the Canary Islands have just given us a slightly new perspective on them.

It’s common knowledge that species living on remote islands evolve in unique ways. They live in isolated environments whose conditions exist nowhere else. In the case of animals that can swim or fly, there’s no great mystery about how they, or rather their distant ancestors, reached the island in the first place. What hasn’t been well understood is how the ancestors of larger species—the giant tortoises of the Galapagos Islands, say—managed the journey.

A new study shows that “mega-landslides” might be responsible. A team led by Brent Emerson from the Institute of Natural Products and Agrobiology in Tenerife “suggests that animals can travel from one land mass to another by floating on giant rafts of earth and vegetation, created by huge landslides.” This would be more plausible, they say, than previous theories that the animals floated on smaller objects such as logs, and it also better explains the migration of species that typically live inland rather than near the shore. “Importantly, big landslides can carry lots of individuals to the same island at once, providing a large and genetically diverse founder population—unlike a small raft such as a floating log.” Large landslides are fairly common on volcanic islands.

Oddly enough, the species that prompted the theory wasn’t something large like a giant tortoise; it was the lowly weevil. Researchers found that weevils on Tenerife are genetically nearly identical to those on La Palma, an island 75 miles away. About 600,000 years ago a large landslide occurred on Tenerife, which “would have carried swathes of relatively intact biomass from the surface of Tenerife out onto the surface of the Atlantic.” It would have taken as long as 13 days for the material to reach La Palma.