|Rock ledges and scarps or any natural overhang in locations such as the Adirondacks in New York or the New River George in West Virginia become draped with icefalls during the winter.
How does an Icefall form? First, there must be an anchor for the icefall. This process begins when the temperature is below freezing and a source of water is available so that Frazil ice (a suspension of small ice crystals which can adhere to grass, soil or rock surfaces) forms as an anchor for grand display to follow. Much as the hanging dam at the eaves of a house roof provide the anchor for icicles - the frazil ice becomes the natural beginning of an icefall. The pillars and curtains of ice that make up an icefall have a washboard surface which appears to be characteristic of these naturally formed vertical sculptures.
The ice that constitutes an icefall is finely polycrystalline and usually shows layering when a thin sample of the ice is viewed under polarized light. The layering is seen as a variation of crystal size across the section and this is related to episodes of additional ice accretion due to rainfall and meltwater. The midwinter warming periods would also be expected to result in the recrystallization of the icefall surface.
When cold water flows from an overhang at subzero temperatures we can always expect icicles to form. Some icefalls look like massive icicles 'glued' together to form a massive curtain of ice. They appear as long sharp cones growing over ten times faster in length than diameter. The growing icicle is not completely frozen, but consists of a long tube of unfrozen water enclosed in ice. Thickness is achieved when a thin film of water flowing down the outside of the icicle freezes. The temperature, wind speed and the amount of water available are incorporated to determine the increase in diameter and length of icicles. Once the basic icefall forms, the details will be determined by the pathways of flowing water that will freeze and add mass to the icefall.
In addition to the water icefall described above - there is also the 'alpine icefall' where ice forms through pressure sintering and recrystallization of snow. This process is signifigantly aided by water which comes in the form of rain and water runoff.