Icicles
by J McCombie
Title
Icicles
Artist
J McCombie
Medium
Photograph - Untouched
Description
This piece has been featured in the FAA Group, "Amateur Photographers ...".
Icicles are one of our strongest symbols of winter and often used to depict the cold depths of prolonged winter. In its basic form, an icicle is a tapered, hanging spike or cone of ice formed by the freezing of dripping or falling water. We mostly think of them as forming off building roofs and edges from melting snow, but icicles can also form on trees, utility poles and fences, and on rocks near waterfalls or ground water seepage points, from rain, mist, spray and water seepage.
Typically, icicles will form when ice or snow is melted by either sunlight or some other heat source (such as a poorly insulated building), and the resulting melted water runs off into an area where the ambient temperature is below the freezing point of water (0 C/32 F), causing the water to refreeze. Over time continued water runoff will cause the icicle to grow.
When the snowmelt flows down the roof, the competition between gravity pulling the water downward and surface tension trying to keep the water flow flat leads to the formation of evenly-spaced ripples along the flow front. These ripples will freeze when and where the surface temperature dips below 0oC (32oF), and the frozen ripples become the icicle roots. Icicles then grow as water dripping over the roots freeze in progressive layers rather than being frozen all at once. This initiates icicle formation.
New icicles are typically cone-shaped, and often small bubbles can be seen within them. As they grow, vertical ridges and horizontal ribs, or rings, form on their outer surface. Icicles grow downward and outward simultaneously but at differing rates. After a period of continuous growth, icicles display prominent horizontal ribbing which encircles the icicle to form a series of progressively smaller rings toward the tip. Each ring is separated from those surrounding it by shallow constrictions in the ice. Typically, rings extend outward less than a centimetre (half an inch). During active icicle growth, the rings are initially composed of fragile, thin ice plates growing randomly outward, but the spaces between them are soon filled with downward flowing meltwater.
Vertical ridges form during renewed growth after a period of dormancy. Melt water streams down the icicle exterior, initially laying a thin track of ice. Continued flow will add additional ice along the same track for as long as the track surface does not completely freeze. Tracks have widths approximately that of the meltwater stream percolating down the icicle. They can build ridges outward half a centimetre (a quarter inch) or more before the water shifts to another track.
The tip of a growing icicle is primarily liquid water with a pendent drop on the tip end. Typically liquid water extends several centimetres (about an inch) up into the interior from the tip. The outer region of the tip is composed of randomly growing ice crystals which meld to form an elongated, inverted cup which is usually filled with liquid water. However, occasionally an air bubble will enter the cup and drain it of liquid. Water flowing along the exterior quickly restores the end drop, trapping some of that air and incorporating it into the solid icicle as a bubble several millimetres (tenths of inches) in diameter. Such bubbles can usually be seen located along the axis of the icicle, giving it a milky appearance.
Even after active growth has stopped, the icicle will continue to change its shape and appearance, even at subfreezing temperatures. Some ice may sublime from solid water to the vapour state, thus slowly altering and smoothing the icicle's surface features. Although icicles can grow to several metres (yards) in length, eventually, melting or gravity will bring an end to the icicle, causing it to fall from its perch and crash onto the surface below. For home and building owners those tapering spikes of ice hanging down from roof edges are common winter problems. They can cause damage to the building since large icicles have the potential to pull down gutters. During thaws or wind storms, falling icicles can be extremely dangerous to people below or vehicles parked next to the overhang. Icicles on roofs are also often associated with ice dams that may cause water to infiltrate under the shingles with possible water damage to the house or building and its contents.
Uploaded
January 19th, 2015
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