The folds of the wild women
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We all certainly heard that the Alps, or even the Himalayas, arose from the collapse of two continents. As a reminder, if two continental plates collide, parts of the plates are unfolded, similar to a carpet that is pushed together from two sides. Now someone may say, "Bending stones, that's just not possible." - but it is important to remember that these processes are extremely slow and / or take place at great depth, where there is high pressure and much heat, so that the rock material becomes soft and flexible. This patterning of rocks happens not only on a large scale, in whole mountains and continents, but also on a small scale. The result can be wonderfully examined by the example of the Wildweiberhöhle.
To be able to record which rocks fold or bend in which way, the different types of folds are named (e.g., folds, creases, and creases) and their geometry determined (e.g., convolution angle, radius at inflection points, or symmetry). On the basis of the following overview (excerpt), the rock fold of the Wildweiberhöhle is to be determined.
The geometric properties of a fold:
• The point with the smallest curvature radius is called a hinge.
• The "straight" section is the thigh.
• Legs of equal length form a symmetrical fold, unequal legs an asymmetrical fold.
• The highest point of a fold is the vertex, the lowest of the trough.
• The point where the direction of curvature changes is the turning point.
• The distance between the trough hinges or the crown hinges is the wavelength,
the perpendicular to the intervening hinge the amplitude.
• The opening angle is determined by the tangents on the legs through the turning points.
• At opening angles of 120 ° -180 °, this is called an open, obtuse fold.
120 ° -70 ° form an open, acute-angled fold.
At 30 ° -70 ° the fold is closed,
Below 30 ° it is called "narrow".
Sources:
Websites: mineralienatlas.de, wikipedia.de (in each case the article about wrinkles)
Book: Treatises of the Royal Prussian Geological Institute, Issue 76, 1913
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