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 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, and many are popular for rock climbing.

Stacks (Rauks) at the island of Fårö east of the mainland of Sweden

Isolated steep-sided, rocky oceanic islets, typically of volcanic origin, are also loosely called "stacks" or "volcanic stacks".

Twelve Apostles, Victoria, Australia-2June2010 (1)
Two of the Twelve Apostles stacks in Victoria, Australia


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 clay—tend to slump and erode too quickly to form stacks, while harder rocks such as granite erode in different ways.)

The formation process usually begins when the sea attacks small cracks in a headland and opens them. The cracks then gradually get larger and turn into a small cave. When the cave wears through the 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.

See also


  1. ^ Easterbrook, D.J. "Surface Processes and Landforms", p. 442, Prentice Hall, Upper Saddle River, New Jersey, 1999.
  2. ^ "Sea stacks" Archived 2009-04-14 at the Wayback Machine

External links

Outline of oceanography

The following outline is provided as an overview of and introduction to Oceanography.

Pinnacle (geology)

A pinnacle, tower, spire, needle or natural tower (German: Felsnadel, Felsturm or Felszinne) in geology is an individual column of rock, isolated from other rocks or groups of rocks, in the shape of a vertical shaft or spire.

Examples are the summits of the Aiguille du Midi in the Mont Blanc massif in France, the almost 43-metre-high Barbarine on the south side of the Pfaffenstein hill near Königstein in Germany, or the Bischofsmütze, the Drei Zinnen and the Vajolet Towers in the Dolomites, which are rich in such towers. An area of limestone formations within Nambung National Park, near the town of Cervantes, Western Australia, are also known as The Pinnacles.


A skerry is a small rocky island, usually too small for human habitation. It may simply be a rocky reef. A skerry can also be called a low sea stack.A skerry may have vegetative life such as moss and small, hardy grasses. They also, in some areas of the world, are rested upon by animals such as seals or birds, though usually not inhabited.


Stump may refer to:

Stump (band), a band from Cork, Ireland and London, England

Stump (cricket), one of three small wooden posts which the fielding team attempt to hit with the ball

A rare tumour of the uterine smooth muscle or prostatic stroma, see STUMP (disambiguation)

Stump (drawing), an artists' drawing tool made of rolled paper

USS Stump (DD-978), a Spruance-class destroyer

Tree stump, the rooted remains of a felled tree

Clussexx Three D Grinchy Glee (born 1998), 2009 "Best In Show" winner at the Westminster Dog Show, nicknamed Stump

The remains of a limb after amputation

A coastal landform which forms when a stack (geology) is eroded

Stump (surname) a surname



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