On February 2, 2020, the falls collapsed into a massive sinkhole behind the layer of hard volcanic rock that formed its lip, creating a large natural bridge spanning the Coca River.

The San Rafael Falls were formed thousands of years ago by debris and lava flows from the nearby El Reventador volcano, whose caldera is located about 9 kilometres (5.6 mi) to the west.

About 19,000 years ago, a large section of the eastern side of the volcano collapsed, causing a massive debris flow of loose rock and soil into the Coca River valley.

The natural impoundment behind the dam eventually filled with a mix of fluvial sediments and additional volcanic material from El Reventador, while the river spilled over the top of the barrier forming a waterfall.

Over thousands of years, the plunge pool at the waterfall base continued to expand, creating a large overhanging precipice and cavern where the hard basalt layer rested atop the loose material below.

On February 2, 2020, the sinkhole abruptly collapsed, swallowing a large portion of the flow of the Coca River, which proceeded to burst out from underneath the lava dam.

By February 6 the remaining loose material under the lava dam had been washed away and the full volume of the Coca River flowed beneath it, creating a massive natural bridge and effectively removing the knickpoint the waterfall represented.

The sudden river rejuvenation initiated headward erosion of the loose unconsolidated sediment in the riverbed, causing the waterfall to quickly retreat upstream.

[2][13][14] In July 2020, five months after the initial collapse, erosion had progressed 3.8 kilometres (2.4 mi) upstream, forming a canyon 100 metres (330 ft) deep in places.

[18][19] By August, bypasses had been constructed to route the oil pipelines away from the river, while downstream communities continued to express concern over the speed of remedial action.

At the outlet of Coca Codo hydroelectric plant, 44.5 kilometres (27.7 mi) downstream, the river bed has risen 1 to 2 metres (3.3 to 6.6 ft),[2] which threatens to limit the amount of water that can pass through the power station and thus its electrical output.

[2] Flooding and water quality impacts tied to the collapse have been reported at Puerto Francisco de Orellana, 90 kilometres (56 mi) downstream from the falls.

[19] Geologist Carolina Bernal stated, "I had doubts that the Coca Codo Sinclair plant influenced what happened with the San Rafael waterfall [on Feb. 2], but now, after seeing the aggressiveness of the phenomenon, it can be linked with the sediment management of the project.