EARTH : marine world " continental drift "

                 The drift of continents:

     >> Is the ground on which we walk as stable as we think? In fact, the contients are always moving under the action of driving forces acting in the depths of the Earth. This displacement of the plates is called continental drift. Rising from the center of the Earth, the intense heat disturbs its rocky surface in the cold. This phenomenon forces the plates, called tectonic plates, to move. Some plates collide, some diverge, and some slide against each other. Depending on the geological time scale, these movements significantly alter the appearance of the Earth. The violent earthquakes and volcanoes are there to remind us dramatically that the plates are always in motion. Each year, the continents drift by about 1 cm!

The tectonic plates:

     Each tectonic plate consists of a lower layer of solid rock and an upper layer called the crust. The plates float on the surface of the mantle which behaves like a very viscous fluid. Where the crust is thin, the surface of the Earth is lower and covered by the seas and oceans. The continents occupy the thicker and higher parts. When the tectonic plates move, they carry the continents with them, and the oceans change shape.

  

the proof!

    In 1915, when Alfred Wegner announced that the continents formed only one large continental mass (the pangea), no one took it seriously. But he was right. Some fossil plants, such as the fern Glossopteris, provided him with proof of his theory: although they were on very distant continents, according to him, they could only come from one and the same continent. Today, geologists have recognized his theory of continental drift.

The collision of the Earth's plates:

    The Andes Cordillera in South America extends its 8,000 km along the Pacific coast. It formed about 170 million years ago, when the Nazca plate collided with and sunk below the South American plate (subduction). The folds indicate where the Earth’s crust folded. About 6 million years ago, the formation of the Andes slowed down.

The tectonic plate boundary:

    When two plates move away from each other, the molten rock ( magma ) rises through the collapse zone that has created. Transformation faults form on either side of the dorsal and cause earthquakes in the case of plates sliding against each other. In the areas of convergence, finally, the colliding plates form a mountain range by bending and elevation of the continental crust.

West of JAVA:

    This photo shows the Anak Krakatoa volcano in Indonesia. It first erupted in 1927 and belongs to a long chain of volcanoes located at the site where the Indo-Australian plate sinks under the Eurasian plate. This subduction plate melts when it enters the Earth’s mantle, causing magma to rise to the surface, forming volcanoes.

Ridge spreading:

    The Mid-Atlantic Ridge is bordered by divergent plates extending from the Arctic to the Southern Ocean. It is largely under the sea, but at Thingvellir, a very volcanic region of Iceland, it rises to the surface. The boundary between the North American marsh and the Eurasian plate is clearly visible. Where the plates have moved away, a valley of collapse, called rift, has formed. In 1963, during a huge underwater volcanic eruption 130 km south of Thingvellir, the lava rose and filled the collapse ditch along the drosale. When it cooled, it formed the new island of Surtsey.