Stack (geology)
A stack or sea stack is a geological landform consisting of a steep and often vertical column or columns of rock in the sea near a coast, formed by wave erosion.[1] Stacks are formed over time by wind and water, processes of coastal geomorphology.[2] They are formed when part of a headland is eroded by hydraulic 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 a natural arch collapses under gravity, due to sub-aerial processes like wind 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 for seabirds,[4] and many are popular for rock climbing, primarily in Ireland.[5]
Isolated steep-sided, rocky oceanic islets typically of volcanic origin, are also loosely called "stacks" or "volcanic stacks".[6]
Formation
Stacks typically form in horizontally bedded sedimentary or volcanic rocks, particularly on limestone cliffs. The medium hardness of these rocks means medium resistance to abrasive and attritive erosion. A more resistant layer may form a capstone. (Cliffs with weaker rock, such as claystone or highly jointed rock, tend to slump and erode too quickly to form stacks, while harder rocks such as granite erode in different ways.)[8]
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The formation process usually begins when the sea attacks lines of weakness, such as steep joints or small fault 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.[9]
See also
- Ball's Pyramid, the tallest sea stack in the world
- List of sea stacks
- Rauk
References
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- ^ Page Module:Citation/CS1/styles.css has no content.Easterbrook, D. J. (1999). Surface Processes and Landforms. Upper Saddle River, New Jersey: Prentice Hall. p. 442. ISBN 0-13-860958-6.
- ^ "Sea stacks" britannica.com Script error: No such module "webarchive".
- ^ Page Module:Citation/CS1/styles.css has no content."Tectonics, Sediment Supply, and Morphologies Along Rocky Coasts | EARTH 107: Coastal Processes, Hazards and Society". courses.ems.psu.edu. Retrieved 2025-11-07.
- ^ Page Module:Citation/CS1/styles.css has no content."Seabirds at Coquille Point". Shoreline Education for Awareness, Inc. 2022-06-12. Retrieved 2025-11-07.
- ^ Page Module:Citation/CS1/styles.css has no content."Sea Stack Climbing Ireland | Climb Donegal's Sea Stacks | Unique Ascent". uniqueascent.ie. Retrieved 2025-11-07.
- ^ Page Module:Citation/CS1/styles.css has no content."Geography and Geology". Lord Howe Island Tourism Association. Archived from the original on 12 September 2014. Retrieved 17 March 2026.
- ^ Page Module:Citation/CS1/styles.css has no content."Mayo - County Geological Site Report" (PDF). Geoheritage. Geological Survey of Ireland. Retrieved 28 December 2023.
- ^ Page Module:Citation/CS1/styles.css has no content.Schwartz, Maurice, ed. (2006). Encyclopedia of Coastal Science. Springer Science & Business Media. p. 238. ISBN 9781402038808.
- ^ Page Module:Citation/CS1/styles.css has no content."WA100: A Washington Geotourism Website". Washington State Department of Natural Resources. Retrieved 17 March 2026.
External links
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- Page Template:Sister-inline/styles.css has no content.Script error: No such module "Sister project logo". Media related to Script error: No such module "Commons link". at Wikimedia Commons
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