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.
What you can do. Use dim red lights for night lights. Red light has the least power to shift circadian rhythm and suppress melatonin. Avoid looking at bright screens beginning two to three hours before bed. If you work a night shift or use a lot of electronic devices at night, consider wearing blue-blocking glasses.ight at night is bad for your health, and exposure to blue light emitted by electronics and energy-efficient lightbulbs may be especially so.