San Rafael Falls

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 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. After that, the volcano erupted and a basaltic lava flow blocked the Coca River, forming a highly erosion-resistant lava dam on top of the initial debris flow deposit. 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. The area around El Reventador remains tectonically active. A March 1987 earthquake caused large debris flows into the Coca River that reached San Rafael Falls. The debris flows reached an estimated depth of at the falls. Prior to the collapse, the falls were a major tourist attraction for the area. In 2019 about 30,000 people visited the falls. The falls were accessible by an approximately thirty-minute hike from nearby Hostería El Reventador (about by road northeast of El Chaco) which brought visitors to a scenic view point, "La Mirador", above the falls. Although located near the Cayambe-Coca National Park, the falls themselves were actually on a small private preserve. In 2010, construction had begun on the Coca Codo Sinclair Dam about upstream from the waterfall. The 1,500 megawatt hydroelectric plant, Ecuador's largest power station, was designed to divert water around a large bend ("codo") of the Coca River, utilizing the natural drop of the waterfall and river to generate power. The developers of Coca Codo Sinclair promised to maintain a minimum flow of over the falls, or about one-quarter of its typical dry season flow. The waterfall had been undergoing noticeable geomorphic changes since the 1990s, when it fell in two distinct stages: a smaller upper cascade followed by a large lower plunge. By about 2010, much of the lower lip of the falls had eroded away, bringing the two tiers close together; in 2015 that section collapsed completely, and the waterfall became a single uninterrupted plunge. ==2020 collapse and impacts==

In June 2019, a sinkhole formed above the falls and water was observed to emerge from the bottom of the cliff face, suggesting that water was seeping through the loose material under the lava dam and thus bypassing the falls. 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. A new waterfall appeared immediately upstream where the sinkhole had been located. The sudden river rejuvenation initiated headward erosion of the loose unconsolidated sediment in the riverbed, causing the waterfall to quickly retreat upstream. In July 2020, five months after the initial collapse, erosion had progressed upstream, forming a canyon deep in places. As the river gradient equalized, the waterfalls evolved from a single plunge to multiple small, separated drops, and eventually were reduced into rapids. Ecuador's Ministry of Energy began constructing temporary grade controls in the river in an attempt to slow the rate of erosion. Erosion soon threatened critical infrastructure upstream. On April 7, 2020, the sinking riverbed broke oil pipelines belonging to the Trans-Ecuadorial Pipeline System, Crudos Pesados Oil and Poliducto Shushufindi-Quito. About 15,000 barrels of crude oil spilled into the Coca River and soon entered the Napo River. Oil was detected as far downstream as Cabo Pantoja, Peru. The oil spill affected more than one hundred primarily indigenous communities, many of which are economically dependent on fishing. On April 30 a lawsuit was filed seeking damages from the oil companies. 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. Large waves of sediment unleashed by the collapse have drastically changed the downstream reaches of the Coca River. About 250 million tonnes (Mt) of sediment was mobilized in the first year after collapse, and by early 2023, three years later, this had increased to 500 Mt. As of 2023, massive aggradation has buried the former riverbed downstream, with sediment piling up as much as at a point below the former waterfall. At the outlet of Coca Codo hydroelectric plant, downstream, the river bed has risen , This has been mitigated so far by dredging, but a long-term solution has yet to be determined. Flooding and water quality impacts tied to the collapse have been reported at Puerto Francisco de Orellana, downstream from the falls. By early 2023, erosion had progressed upstream from the original waterfall location. Some of riverside land have collapsed and at least three bridges have been destroyed. Headward erosion is expected to continue for another before the river achieves a stable gradient, which would be more than enough to reach the Coca Codo Sinclair Dam, unless the river encounters a harder rock layer before that point. The headward erosion has also begun to affect tributaries, particularly the Río Malo, which joins the Coca about upstream from the former waterfall. ==Investigation==

While all waterfalls experience headward erosion, many researchers and groups have suggested that the Coca Codo Sinclair Dam may have increased the effect of erosion on the falls, causing it to collapse sooner than from natural geologic forces alone. Emilio Cobo, leader of the IUCN's South America Water Program, surmised that the dam accelerated the collapse by trapping sediment upstream, starving the river of sediment and increasing its erosive force. According to Alfredo Carrasco, an Ecuadorian state geologist, the collapse of the waterfall was probably not significantly affected by damming, but the rapid riverbed erosion that followed was made worse by the dam. After the collapse, Carrasco had expressed concern over the potential impact on infrastructure such as bridges and oil pipelines, but no remedial action was taken before that infrastructure was undermined and destroyed. 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. Hydroelectric plants must be planned very carefully." ==See also==