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.
Nobody likes being blinded when riding or driving at night, and as bike light LEDs get brighter and brighter, this is increasingly a concern for road users of all types. Most bike lights, even those costing hundreds of dollars, have symmetrical beams which shine equal amounts of light above and below the device.