San Rafael Falls (Spanish: Salto de San Rafael) was a waterfall on the Coca River in Sucumbíos and Napo, Ecuador. Standing 131 metres (430 ft) high, it was the tallest and most powerful waterfall in Ecuador and a popular tourist attraction. The falls were located at the eastern boundary of Cayambe Coca National Park, in the eastern Andean foothills about 170 kilometres (110 mi) to the east of Quito. 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 natural bridge also collapsed about one year later, leaving an open ravine at the former site of the falls. During its brief existence, the natural bridge may have been the longest in the world, exceeding China's Xianren Bridge. The waterfall itself retreated upstream as a result of rapid headward erosion and disappeared within a few months as the river carved a new, more gradually descending channel. The collapse of the falls has significantly altered the Coca River, with a deep new canyon appearing upstream of the former falls, and large volumes of sediment depositing downstream. Upstream erosion destroyed several bridges and oil pipelines, and as of 2023 threatens to undermine the Coca Codo Sinclair Dam, which was built upstream of the falls in 2016. Increased erosion as a result of the dam trapping sediment is thought by some researchers to have accelerated the collapse of the waterfall, although the phenomenon would likely have happened eventually due to the natural erosive force of the river.
History 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. After that, the volcano erupted and a 100-metre-thick (330 ft) 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 debris flow material downstream of the lava dam washed away, increasing the drop to over 130 metres (430 ft). 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. At this point, the knickpoint became relatively stable, with the overhanging basalt protecting the loose material below from further upstream erosion. 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 20 metres (66 ft) 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 50 kilometres (31 mi) 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 19 kilometres (12 mi) 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. Despite creating significant controversy over its ecological impact and its potential to reduce the flow of the waterfall, the project was completed in 2016. The developers of Coca Codo Sinclair promised to maintain a minimum flow of 22 cubic metres per second (780 cu ft/s) 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.
… excerpt ends here. Continue reading the full article.
