6-510: Lange Anna ("Tall Anna"), is a 47-metre-high (154 ft) sea stack of Buntsandstein in the North Sea island of Heligoland , Germany . Its local name is Nathurn Stak ("Northern Stack"). Climbing the stack is not allowed but tourists may view the rock from a distance. Lange Anna is somewhat similar to the Old Man of Hoy or Old Harry . In 1969 it was declared a natural monument . The stack
12-406: 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.) 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
18-491: A stump. Stacks can provide important nesting locations for seabirds , and many are popular for rock climbing . Isolated steep-sided, rocky oceanic islets typically of volcanic origin, are also loosely called "stacks" or "volcanic stacks". 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
24-415: 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 . Stacks are formed over time by wind and water, processes of coastal geomorphology. 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
30-613: Is subject to severe weathering wear and decomposition. It was decided that any further effort for its conservation could do nothing but slow down the process, so the Lange Anna today is consigned to its fate. Experts assume an acute danger of collapse of the top two thirds because of an unstable layer of sands 16 metres (52 ft) above sea level, which already is the thinnest part of Lange Anna. 54°11′18″N 7°52′11″E / 54.1882°N 7.8698°E / 54.1882; 7.8698 Stack (geology) A stack or sea stack
36-427: 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
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