A crevasse is a deep crack, or fracture, found in an ice sheet or glacier, as opposed to a crevice that forms in rock. Crevasses form as a result of the movement and resulting stress associated with the shear stress generated when two semi-rigid pieces above a plastic substrate have different rates of movement. The resulting intensity of the shear stress causes a breakage along the faces.
Unfortunately, many cyclists choose to ride their bikes at dark without bicycle head lights or tail lights. This is against the law in most states in the U.S. (Amazingly, Washington, Texas, and others only require a head light and rear reflector.) It is also very dangerous.here are at least two primary reasons for you, a bicycle rider, to use lights at night. 1  First, the front head light illuminates the area in front of you, so you can ride safely, by being able to detect any hazards you approach.
Proper Positioning. Bicycle reflectors reflect the upper beam of a carâs headlamps. To ensure you are visible on the road at night, position your safety equipment properly. Rear reflectors, for example, should point straight back.Inspect all installations regularly, tightening loose screws that can cause reflectors to move out of place.t night, a reflector makes you visible from 500 feet way, giving a car going at 60 mph about twice the distance it needs to come to a stop. On the other hand, if you forgo reflectors and wear blue or black, you become noticeable at 55 feet of distance, allowing a driver less than one second to react after he sees you.