reach sizes of even at large distances from Parinacota. These large blocks dominate the avalanche deposit; fine material is not present in the Parinacota collapse deposit, an unusual feature among debris avalanches. Some blocks slid away from the main avalanche deposit. The avalanche deposit displays a noticeable split into two units; the upper one is andesitic and originated from the actual cone, the lower one is derived from the lava domes beneath the present-day edifice. This collapse gave birth to Lake Chungará when the avalanche flowed across a westbound drainage between Choquelimpie and Parinacota, forming a high volcanic dam that retained about of water. The formation of lakes during sector collapses has been observed at other volcanoes, including the 1988 Mount St. Helens collapse. Prior to the collapse, alluvial and riverine deposits occupied the area. In 2015 it was proposed that a much smaller lake occupied part of the Lake Chungará basin before the collapse. Within the hummock-like topography of the deposit, a number of other lakes and peat filled basins are found, formed by water percolating through the avalanche deposit. These lakes are known as the Lagunas Cotacotani lakes, and are an important bird refuge. At least some of these lakes may be kettle holes, formed when blocks of ice transported within the avalanche melted. With increasing distance from the main cone the size of the lakes decreases. Some of these lakes are connected with each other and others are isolated, and during periods of low lake stands some of the lakes can become disconnected from each other. Springs at the foot of Parinacota form the Rio Benedicto Morales which flows through some of the lakes and ends in the main Lake Cotacotani. Otherwise, these lakes receive water from Lake Chungará through seepage. The lakes ultimately form the headwaters of the Rio Lauca, whose course previously extended across the area covered by the avalanche. The river has not carved an outlet all the way to Lake Chungará, probably because the relatively coarse avalanche deposit allows large amounts of water to seep through without carving a new river channel. The rate at which waters seep through the avalanche deposit has been estimated at ; it has progressively decreased over time, probably as a consequence of increased siltation within the avalanche deposit. Thus the depth and surface area of Lake Chungará have increased since the formation of the lake, and so