Why Did Ecuador's Largest Waterfall Disappear?

The San Rafael waterfall shown in 2012. But earlier this year, the waterfall had almost completely stopped flowing. (Photo: Ministerio de Turismo Ecuador [CC BY-SA 2.0]/Flickr)

Earlier this year, the 500-foot-tall San Rafael waterfall in the Ecuadorian Amazon seemed to vanish. The country's largest waterfall in both height and volume, its disappearance wasn't caused by a sudden drop in water levels, but instead because the Coca River decided to literally "drop." A few meters behind the waterfall, a gigantic hole opened up, changing the riverbed and diverting the river through a nearby arch that survived the collapse.

Drone footage shows both before and after scenes of the waterfall's incredible transformation. Sadly, especially for the tour groups that annually flocked to the site, the new hole has reduced the original iconic waterfall to little more than a trickle.

A natural or man-made phenomenon?

Exactly why the Coca River suddenly tunneled through its riverbed is a hotly debated topic between geologists and conservationists. An expose in Mongabay on the waterfall's disappearance quoted Alfredo Carrasco, a geologist and former secretary of Natural Capital at the ministry, as saying that the San Rafael's location within a volcanic and earthquake-prone region likely played a role.

"There are many quite intense earthquakes here. In March 1987, a very strong one appeared that caused tremendous damage to the trans-Ecuadorian oil pipeline that passes right through it," he said. "That year I had the opportunity to evaluate the impact of the earthquake in that area. There were floods of up to 20 meters above the level of the valley where the river passes."

The San Rafael waterfall before its transformation on Feb. 2, 2020.
The San Rafael waterfall before its transformation in February 2020. (Photo: Cesar Girolimini/Shutterstock)

Carrasco added that floods and lava from an eruption of the nearby Reventador volcano in 2008 likely caused a natural damming of the river, which may have led to extreme erosion at its base and the formation of the new falls under the arch.

"It is very typical that the energy of the water falling erodes the base," he said. "For me, the phenomenon [the collapse of the waterfall] is eminently of natural origin."

Others, however, point to the existence of the new Coca Codo Sinclair hydroelectric plant, which sits about 20 kilometers upstream of the San Rafael waterfall as a possible culprit. Emilio Cobo, coordinator of the South America Water Program at the International Union for the Conservation of Nature (IUCN), tells the site that it's possible the hydroelectric plant may have indirectly caused the waterfall's demise via a phenomenon called "hungry waters."

"When a river loses sediments, water increases its erosive capacity, an effect called 'hungry waters'," Cobo said. "All rivers carry eroded sediments from the soils and rocks on which they pass. All dams and reservoirs trap part of this sediment, especially heavy materials, and thus deprive the downstream river of its normal sediment load."

Cobo believes it's no coincidence that the riverbed eroded only a few years after the hydroelectric plant opened. "These are processes that are in scientific papers and there is sufficient evidence that a dam can cause effects of this type on a river," he added.

Officials plan on continue studying the collapse of the San Rafael falls to determine the exact cause, as well as to monitor the near-certain risks for future erosion and increased landslides along the river. One thing that's known for sure: Agoyan Waterfall, once Ecuador's second-largest waterfall, is now the new reigning champ.