Stack (geology)
Steep rock column in the sea formed by coastal erosion.
A stack, or sea stack, is a steep, vertical column of rock standing in the sea near a coast, formed by wave erosion. These landforms arise when part of a headland is eroded by hydraulic action, causing cracks to widen and eventually collapse. Stacks can provide important nesting sites for seabirds and are popular for rock climbing, particularly in Ireland.
Quick Facts
- Erosion processes
- Hydraulic action
- wind erosion
- sub-aerial processes
- Formation sequence
- Cracks
- caves
- arch
- stack
- stump
Facts from the source article.
Formation
Stacks typically develop in horizontally bedded sedimentary or volcanic rocks, particularly on limestone cliffs, where medium hardness offers medium resistance to erosion. A more resistant layer may form a capstone. The process begins when the sea attacks lines of weakness such as steep joints or small fault zones, enlarging them into caves. If a cave wears through a headland, an arch forms; further erosion causes the arch to collapse, leaving a free-standing stack. Eventually, erosion reduces the stack to a stump, a small rock island often submerged at high tide.
More in Coastal Landforms
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