Cliffs form through tectonic activity, water movement, weathering, erosion and glacier activity. Earthquakes and landslides also form cliffs. Cliffs tend to form on coasts, in mountainous areas, along rivers or as the walls of canyons.
Pressure builds when tectonic plates beneath the Earth's surface rub together. Eventually, this pressure pushes one or both plates upward, causing earthquakes and landslides that gradually form cliffs and mountains. The tallest known cliff, the Rupal Flank in the Himalayas, formed due to tectonic pressure.
Wind, rain and wave activity form cliffs as well. Erosional weathering wears down and breaks apart existing rocks and mountains. The rock left behind is stronger than most rock and typically vertical. Wave activity from rivers and oceans form cliffs by cutting into rock continuously over millions of years. The Colorado River formed the Grand Canyon in this way, and the Great Lakes also formed many cliffs.
During ice ages, glaciers form cliffs by grinding against rock as they shift across the planet's surface. Glaciers formed the Fones Cliffs millions of years ago when Virginia's Northern Neck area was submerged underwater. Due to the size of glaciers, the cliffs they create are typically larger than those formed by erosion or weathering.