Plate Tectonics, Earthquakes and Volcanoes - Class VIII

There are no volcanoes on the Australian mainland that have erupted since European settlement, but some volcanoes in Victoria, South Australia, and North Queensland were witnessed by Aboriginal people several thousand years ago.

The Pacific Ring of Fire, which includes the west coasts of North and South America and the eastern coastal areas of Asia, is the region with the highest frequency of earthquakes.

An earthquake is the shaking of the surface of the Earth resulting from a sudden release of energy in the Earth's lithosphere that creates seismic waves.

An earthquake's point of initial rupture is called its focus or hypocenter. The epicenter is the point at ground level directly above the hypocenter.

Molten rock located beneath the Earth's surface is called magma. Once it erupts onto the surface, it is referred to as lava.

The Himalayas are generally divided into three ranges which are Siwalik, Greater Himalayas and Lesser Himalayas. The Karakoram or Karakorum is a large mountain range spanning the borders of Pakistan, India, and China, with the northwest extremity of the range extending to Afghanistan and Tajikistan.

Tectonic plates are part of the lithosphere, which floats on the semi-fluid, ductile layer of the Earth known as the asthenosphere, located within the upper mantle.

The movement of tectonic plates is due to the enormous amount of thermal energy generated in the inner core and transferred to the mantle thus, causing movement in the tectonic plates.

Plate collisions occur at convergent boundaries, which can happen on continental landmasses (forming mountain ranges like the Himalayas) or on the ocean floor (forming deep-sea trenches and island arcs).

At a transform plate boundary, tectonic plates slide horizontally past one another. Crust is neither created nor destroyed at these boundaries.

A subduction zone is a geological process that takes place at convergent boundaries of tectonic plates where one plate moves under another and is forced to sink due to high gravitational potential energy into the mantle.

Geological evidence indicates that the Indian Plate was part of the supercontinent Gondwanaland approximately 250 million years ago before it began its northward drift.

The Indian Plate was part of the supercontinent Gondwanaland. It began to break away and drift northward approximately 140 million years ago.

Gondwanaland was a supercontinent that included modern Africa, South America, Antarctica, Australia, and the Indian subcontinent. Since all listed options are parts of the former Gondwanaland, 'All of these' is the correct choice.

Continental plates are composed primarily of granitic rocks, which are less dense and thicker than the basaltic rocks that make up oceanic plates. Because they are less dense, they 'float' higher on the mantle, resulting in greater thickness.

The Great Rift Valley is formed by the divergence of tectonic plates, which causes the crust to crack and drop down between parallel faults. This process is known as faulting.

Tectonic plates move at varying speeds, but the average rate of movement for major plates is generally cited as approximately 2.5 cm per year.

At a convergent boundary, two tectonic plates move toward each other. This interaction often leads to subduction or mountain building.

Currently, geologists are working on the theory of plate tectonics. Geologically speaking, a "plate" is a large, rigid slab of rock. The theory of plate tectonics states that the earth's outermost, rigid layer, the lithosphere, is fragmented into a dozen or more irregularly shaped plates that are riding atop a hotter, more mobile material, the asthenosphere.

There are three kinds of plate tectonic boundaries: divergent, convergent, and transform plate boundaries. A divergent boundary occurs when two tectonic plates move away from each other. When two plates come together, it is known as a convergent boundary. 

 The word Epeirogenetic consists of two words viz, 'epiros' means continent and 'genesis' means origin. So eperiogenetic movement gives rise to the continent. Epeirogenetic movement causes upliftment  and subsidence of continental masses through upward and downward movements respectively. Both, the movements are vertical movement. 

The Powerful internal forces operating from within the crust are called Earth Movements which bring about vast changes on the earth's surface are called Earth Movements. They may be slow and sudden. Slow movements occurs at a very slow rate and continue much longer as compared to our life span. These movements are relative to each other, the land advancing against sea is termed as negative movement and the sea advancing on land is known as positive movement.

Mountain and continents are formed due to slow earth movement. Slow forces include both vertical and horizontal movements which are caused due to forces deep within the earth. These forces operate very slowly and their effects become discernible after thousands and million of year. 

The Earth's surface relief is shaped by both internal (endogenic) forces like tectonic activity and external (exogenic) forces like weathering and erosion, which are known as gradational forces.

There are seven main or “primary” tectonic plates: these are the African Plate: Antarctic Plate, Eurasian Plate, Indo-Australian Plate, North American Plate, Pacific Plate, and South American Plate.

In Sutlej valley the Himalayan pass Shipki La is located. A spur road on the Indian side rises to an altitude of 4,720 metres (15,490 ft) four km southwest of Shipki La. It is located in Kinnaur district in the state of Himachal Pradesh, India, and Ngari Prefecture in Tibet, China.

             Mountain passes in Himalayas             States

The Indian subcontinent was part of the southern supercontinent Gondwana before it broke away and drifted north to collide with the Eurasian plate.

Vertical movements are responsible for the rise or fall of a portion of the earth surface. Vertical movements of the earth do not disturb the horizontality of the strata. Vertical movements cause uplift and subsidence.

The word Orogeny is derived from a Greek word 'Oros' meaning mountain. The orogenic movements are due to horizontal forces in earth's crust, as a result of which rock-strata are crumpled and folded. It is this movement that give rise to mountains.

Asia is separated from Europe by the Ural mountains on the west (Figure 5.1). The combined landmass of Europe and Asia is called Eurasia (Europe + Asia).

Young folded mountains, such as the Himalayas, are located at active plate boundaries where crustal deformation is ongoing, making them the most prone to earthquakes compared to stable old shields or plains.

Igneous rocks are formed from the cooling and solidification of molten rock (magma or lava), which originates from volcanic activity.