San Rafael, Cascada de

Cascada de San Rafael, or San Rafael Falls, was formerly one of the most significant waterfalls in the world when taking into account its combined height and volume. The falls occurred along the Rio Coca and were said to drop 130 meters (430 feet) in two steps, with the largest drop falling just under 100 meters. The falls were formed presumably tens of thousands of years ago by a volcanic dike extruded into the river valley by the adjacent Reventador volcano, one of the most active in the world. Prior to the construction of the Coca Codo Sinclair Dam approximately 20 kilometers upstream from the falls, the volume of water passing over the cataract averaged approximately 14,000 cubic feet per second, but after the dam came online the volume of water was considerably reduced.
In mid 2008, part of the cliff forming the falls began to cleave and fall into the amphitheater below, which resulted in the separation between the two steps of the falls being noticeably reduced. A much larger collapse of the cliff face occurred between July and October of 2015, which resulted in the step separating the two tiers of the falls disappearing entirely, with the falls reverting to a single plunging tier. The exact date of this event is not clear, but photos found online dated prior to July 2015 show this to be the approximate period.
In February 2020 a sinkhole opened in the riverbed immediately upstream of the waterfall, which allowed the river to erode into the ground behind the dike which created the waterfall, and eventually caused a massive collapse of earth behind the waterfall which led to the river entirely bypassing the previous location of the falls, and tunneling beneath the cliff which formed the falls, creating a massive natural bridge in the process. The waterfall then migrated approximately 200-300 meters further upstream from its previous location, but because of the considerable volume of the river the canyon which was quickly eroded still resulted in a fall of over 100 meters in height. Since February of 2020, the Rio Coca has aggressively eroded the riverbed upstream from the former site of San Rafael Falls, and the resulting canyon has lengthened to over four kilometers from the site of the falls, and as a result San Rafael Falls itself no longer exists.
As the river continues to erode the valley floor there have been several smaller waterfalls which have been exposed due to harder layers of rock and soil which have been encountered. Through this entire length of river there are not thought to be any similar volcanic dikes which would impede the flow similar to that which formed San Rafael Falls, which is why the river has so quickly eroded the canyon so far upstream. As of the end of 2020, the waterfall at the head of the new canyon may be 30-35 meters in height, but as the soil in the area is unstable and easily eroded, it is not expected to persist long term, and it may only be a matter of time before any semblance of waterfalls along this stretch of the Rio Coca are gone forever.
Of geological note, at the location of the former falls, the natural bridge which was left standing - as long as it remains standing - is now home to a singularly unique phenomena. A tributary stream formerly entered the Rio Coca in between the two tiers of San Rafael Falls, and following the first cliff collapse in 2015 it began to pour directly into San Rafael Falls itself. Following the collapse in 2020, this stream now falls down the former path of San Rafael Falls, but only after traversing laterally across the top of the natural bridge first. There may not be anywhere else on earth where a stream crosses over the top of another watercourse via a natural bridge.