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- اقتلاع الجليد للصخور (Plucking) هي ظاهرة جليدية تتسبب في تآكل ونقل صخر الأديم. ومع تحرك النهر الجليدي إلى أسفل الوادي، يحدث احتكاك مع قاع الصخور. ويتسبب هذا الاحتكاك في ذوبان الثلج القاعدي للنهر الجليدي وتخلله الفواصل في صخر الأديم حيث تتجمد بعد ذلك. وبينما يتحرك النهر الجليدي، يلتصق الصخر الآن بالنهر الجليدي ويُقتلع من صخر الأديم إلى قاعدة النهر الجليدي ويحمله معه. ويمكن أن تتسبب هذه الصخور المقتلعة أيضًا في سحج صخر الأديم والجدران. يستغل اقتلاع الجليد للصخور الشقوق الموجودة سابقًا في صخر الأديم. ويلعب ذلك دورًا رئيسيًا في فتح وتكوين شقوق جديدة، ولكنه وفر فقط قطعًا صغيرة من المادة الصخرية المفككة. ويتبع ذلك تآكل الصخور المفككة بواسطة الجليد. وخلال عملية التآكل، تتجمد المادة الصخرية المفككة في قاعدة النهر الجليدي وتندمج مع الثلج الجليدي. وهذه العملية مهمة عندما يكون صخر الأديم مفصليًا للغاية؛ حيث يسمح ذلك لماء الجليد المنصهر بالاختراق. ويُعرف اقتلاع الجليد للصخور أيضًا باسم المقلع (quarrying). (ar)
- Plucking, also referred to as quarrying, is a glacial phenomenon that is responsible for the weathering and erosion of pieces of bedrock, especially large "joint blocks". This occurs in a type of glacier called a "valley glacier". As a glacier moves down a valley, friction causes the basal ice of the glacier to melt and infiltrate joints (cracks) in the bedrock. The freezing and thawing action of the ice enlarges, widens, or causes further cracks in the bedrock as it changes volume across the ice/water phase transition (a form of hydraulic wedging), gradually loosening the rock between the joints. This produces large pieces of rock called joint blocks. Eventually these joint blocks come loose and become trapped in the glacier. In this way, plucking has been linked to regelation. Rocks of all sizes can become trapped in the bottom of the glacier. Joint blocks up to three meters have been "plucked" and transported. These entrained rock fragments can also cause abrasion along the subsequent bedrock and walls. Plucking also leads to chatter marks, wedge shaped indentations left on the bedrock or other rock surfaces. Glacial plucking both exploits pre-existing fractures in the bedrock and requires continued fracturing to maintain the cycle of erosion. Glacial plucking is most significant where the rock surface is well jointed or fractured or where it contains exposed bed planes, as this allows meltwater and clasts to penetrate more easily. Plucking of bedrock also occurs in steep upland rivers, and shares a number of similarities with glacial examples. In such cases, the loosening and detachment of blocks appears to result from a combination of (1) chemical and physical weathering along joints, (2) hydraulic wedging driven by smaller rock fragments getting into existing cracks, (3) crack propagation from stresses caused by impacts of large clasts already in transport by the river, and possibly (4) crack propagation driven by flexing resulting from pressure variation in the overlying water during floods. Loosened blocks are then carried away by fast flowing water during large floods, though the entrainment is believed to be significantly less efficient than the equivalent ability of ice to carry away blocks under glaciers. (en)
- Une excavation glaciaire est une conformation concave du sol abritant une partie d'un glacier. Elle se forme depuis une fracture préexistante du substrat rocheux et joue un rôle important dans son extension et la formation de nouvelles fractures d'où ne sont issus que de minimes fragments de matière, déplacés ensuite par le glacier, à la base duquel ils s’incorporent par l’effet de la congélation. Le phénomène est d’autant plus marqué que la roche présente d’importantes fractures qui permettent à l’eau de fusion de s’y infiltrer puis de la faire éclater sous l’effet du gel. Quand le glacier se déplace dans la vallée, le contact de sa base sur le sol provoque la fonte de la surface en contact, agissant à la fois alors comme un lubrifiant et permettant ainsi à l’eau de fonte de s’infiltrer dans les failles du terrain rocheux ; recommençant ainsi le cycle de l’excavation et propulsant en aval du glacier une masse de débris rocheux. (fr)
- L'escavazione glaciale (in lingua inglese plucking, quarrying) sfrutta le fratture preesistenti nel substrato roccioso e svolge un ruolo chiave nell'allargamento e nella formazione di nuove fratture, fornendo però solo piccoli segmenti di materiale incoerente. L'escavazione è dunque seguita dal trasporto di sedimenti della roccia staccati dal ghiaccio. Durante il trasporto il materiale roccioso staccato viene a congelarsi alla base del ghiacciaio nel quale si incorpora. È determinante che la roccia in posto sia fortemente fratturata, sì da permettere all'acqua di fusione di penetrare. Quando la colata si muove a valle vi è attrito con la superficie della roccia. Questo fa sì che il ghiaccio basale del ghiacciaio fonda (aiutando così a lubrificarne il movimento), infiltrandosi nelle fratture del substrato roccioso dove quindi congela. Il movimento della colata fa sì che la roccia, adesso ancorata al ghiacciaio molto più fermamente, venga strappata dal suo strato e trasportata a valle. (it)
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- اقتلاع الجليد للصخور (Plucking) هي ظاهرة جليدية تتسبب في تآكل ونقل صخر الأديم. ومع تحرك النهر الجليدي إلى أسفل الوادي، يحدث احتكاك مع قاع الصخور. ويتسبب هذا الاحتكاك في ذوبان الثلج القاعدي للنهر الجليدي وتخلله الفواصل في صخر الأديم حيث تتجمد بعد ذلك. وبينما يتحرك النهر الجليدي، يلتصق الصخر الآن بالنهر الجليدي ويُقتلع من صخر الأديم إلى قاعدة النهر الجليدي ويحمله معه. ويمكن أن تتسبب هذه الصخور المقتلعة أيضًا في سحج صخر الأديم والجدران. (ar)
- Plucking, also referred to as quarrying, is a glacial phenomenon that is responsible for the weathering and erosion of pieces of bedrock, especially large "joint blocks". This occurs in a type of glacier called a "valley glacier". As a glacier moves down a valley, friction causes the basal ice of the glacier to melt and infiltrate joints (cracks) in the bedrock. The freezing and thawing action of the ice enlarges, widens, or causes further cracks in the bedrock as it changes volume across the ice/water phase transition (a form of hydraulic wedging), gradually loosening the rock between the joints. This produces large pieces of rock called joint blocks. Eventually these joint blocks come loose and become trapped in the glacier. (en)
- Une excavation glaciaire est une conformation concave du sol abritant une partie d'un glacier. Elle se forme depuis une fracture préexistante du substrat rocheux et joue un rôle important dans son extension et la formation de nouvelles fractures d'où ne sont issus que de minimes fragments de matière, déplacés ensuite par le glacier, à la base duquel ils s’incorporent par l’effet de la congélation. Le phénomène est d’autant plus marqué que la roche présente d’importantes fractures qui permettent à l’eau de fusion de s’y infiltrer puis de la faire éclater sous l’effet du gel. (fr)
- L'escavazione glaciale (in lingua inglese plucking, quarrying) sfrutta le fratture preesistenti nel substrato roccioso e svolge un ruolo chiave nell'allargamento e nella formazione di nuove fratture, fornendo però solo piccoli segmenti di materiale incoerente. L'escavazione è dunque seguita dal trasporto di sedimenti della roccia staccati dal ghiaccio. Durante il trasporto il materiale roccioso staccato viene a congelarsi alla base del ghiacciaio nel quale si incorpora. È determinante che la roccia in posto sia fortemente fratturata, sì da permettere all'acqua di fusione di penetrare. (it)
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- اقتلاع الجليد للصخور (ar)
- Excavation glaciaire (fr)
- Escavazione glaciale (it)
- Plucking (glaciation) (en)
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