 | This articleneeds additional citations forverification. Please helpimprove this article byadding citations to reliable sources. Unsourced material may be challenged and removed. Find sources: "Stack" geology – news ·newspapers ·books ·scholar ·JSTOR(August 2015) (Learn how and when to remove this message) |
Astack orsea stack is ageologicallandform consisting of a steep and often vertical column or columns of rock in the sea near a coast, formed bywave erosion.[1] Stacks are formed over time by wind and water, processes of coastal geomorphology.[2] They are formed when part of aheadland iseroded byhydraulic action, which is the force of the sea or water crashing against the rock. The force of the water weakens cracks in the headland, causing them to later collapse, forming free-standing stacks[3] and even a small island. Without the constant presence of water, stacks also form when anatural arch collapses undergravity, due tosub-aerial processes likewind erosion. Erosion causes the arch to collapse, leaving the pillar of hard rock standing away from the coast—the stack. Eventually, erosion will cause the stack to collapse, leaving a stump. Stacks can provide important nesting locations forseabirds,[4] and many are popular forrock climbing, primarily in Ireland.[5]
Isolated steep-sided, rocky oceanicislets typically of volcanic origin, are also loosely called "stacks" or "volcanic stacks".
Stacks typically form in horizontally beddedsedimentary orvolcanic rocks, particularly onlimestone cliffs. The medium hardness of these rocks means medium resistance to abrasive and attritiveerosion. A more resistant layer may form acapstone. (Cliffs with weaker rock, such asclaystone or highly jointed rock, tend toslump and erode too quickly to form stacks, while harder rocks such asgranite erode in different ways.)[7]
The formation process usually begins when the sea attacks lines of weakness, such as steepjoints or smallfault zones in a cliff face. These cracks then gradually get larger and turn into caves. If a cave wears through a headland, an arch forms. Further erosion causes the arch to collapse, leaving the pillar of hard rock standing away from the coast, the stack. Eventually, erosion will cause the stack to collapse, leaving a stump. This stump usually forms a small rock island, low enough for a high tide to submerge.
Media related toGeological stacks (category) at Wikimedia Commons
