Surface markings associated with an advance of a fatigue crack in a single load cycle Not usually visible to the naked eye Their absence at high magnification does not exclude a fatigue mechanism
Scratches or grooves gouged into surface rock by glacial action Striations along bedrock indicate direction of ice movement Often seen on exposed bedrock Photo
Grooves or channels in cloud formations, arranged parallel to the flow of air and therefore depicting the airflow relative to the parent cloud Striations often reveal the presence of rotation, as in the barber pole or "corkscrew" effect often observed with the rotating updraft of an LP storm