Earth's Dynamic Processes: Earthquakes, Volcanoes, and Plate Tectonics

Earthquakes and Volcanoes

Earthquakes

An earthquake is a violent trembling of the Earth's crust, lasting a short time and varying in intensity. It occurs when materials abruptly fracture within the lithosphere. The point of origin is called the hypocenter. From the hypocenter, freed energy transmits as seismic waves in all directions. The most affected surface point is the epicenter. Energy transmits in superficial seismic waves.

Volcanoes

Volcanoes expel extremely hot materials. A volcano is an opening in the Earth's crust through which melted rocky materials from inside the Earth are expelled. This material is called magma within the crust and lava once expelled.

Continental Drift and Plate Tectonics

Continental Drift

Alfred Wegener proposed the theory of continental drift. Initially, a single landmass called Pangea existed, which later fragmented. Evidence includes the matching coastlines of western Africa and eastern South America.

Plate Tectonics

The theory of plate tectonics explains that the Earth's surface comprises fragments called lithospheric plates, continuously moving and colliding. These movements result from the planet's internal energy.

Types of Plates

• Oceanic plates: Form at the ocean floor and part of the upper mantle, with an average crustal thickness of 5-7 km.
• Continental plates: Form the continents, composed of continental crust, 30-40 km thick (up to 60 km in high mountain ranges).
• Mixed plates: Contain both oceanic and continental crust, with emerged (continental) and submerged (oceanic) parts.

Plate Boundaries

• Convergent: Plates move towards each other.
• Divergent: Plates move apart.
• Transform faults: Plates slide past each other.

Examples of Plate Boundaries

Divergent Boundary in the Atlantic Ocean

The Atlantic Ocean exhibits significant volcanic activity. Melted materials are continuously expelled and cool to form the oceanic crust. The land is displaced on both sides of the mid-ocean ridge. Many such ridges on Earth's crust represent divergent boundaries.

Convergent Boundaries in Asia

The Pacific oceanic plate collides with the Eurasian continental plate. The Indo-Australian plate also collides with the Eurasian plate, but neither subducts under the other. This collision uplifts the land, forming the Himalayas.

Rock Formation

Igneous Rocks

Igneous rocks form from the cooling and solidification of magma.

• Extrusive (volcanic): Solidify rapidly, e.g., basalt.
• Intrusive: Cool slowly within the Earth's crust, e.g., granite.

Metamorphic Rocks

are formed by alteration of other rocks, due to increases in temp or pressure, or both at the same time. Metamorphism is the name given to the set of processes involved in these tranformations. Regional metamorphism, when te volume of the rocks affected includes a region covering 100s or 1000s km. Local M.., when the numbre of rocks affected is much smaller