Landforms of the Earth and Internal Forces - Class-IX

The Earth's axis is tilted at an angle of 23.5 degrees. As the Earth revolves around the Sun, this tilt causes different hemispheres to receive varying amounts of direct sunlight throughout the year, resulting in seasons.

Focus is the place where an earthquake originates the focus is also called the hypocenter of an earthquake. The earthquake waves start at the focus and travel outward in all directions.

Earthquake is a natural disaster in which Earth surface shakes. In case of an earthquake, if a person is indoor, he should stay inside and take cover under a table or other furniture, and if a person is outdoor he should stay away from the things that can fall and injure him, like trees and building.

• A geyser is a vent in Earth's surface that periodically ejects a column of hot water and steam. They are a quite rare phenomenon on Earth due to the precise conditions that are required for them to form. They are mainly clustered near active volcanic areas. 
• The Taupo Volcanic Zone in New Zealand is 350 km long and 50 km wide and contains volcanoes, hot springs and geysers. The largest geyser ever known, the Waimangu Geyser, sat in the Taupo Volcanic Zone.

The Richter scale is logarithmic. Each whole number increase in magnitude represents a tenfold increase in measured amplitude. Therefore, a magnitude 3 earthquake is 10 * 10 = 100 times stronger than a magnitude 1 earthquake.

Weak zones in the Earth's crust where tectonic plates meet or shift are known as both seismic zones and fault zones. These areas are highly susceptible to earthquake activity.

The plateau of India is roughly triangular in shape.

The Earth's crust is divided into the Sial (Silica and Aluminium) layer, which primarily forms the continents, and the Sima (Silica and Magnesium) layer, which forms the ocean floors.

The scientific theory that explains how Earth's lithosphere is divided into large plates that move slowly across the mantle is called plate tectonics. Continental drift was an earlier hypothesis proposed by Alfred Wegener.

The Richter scale is a standard measure used to quantify the magnitude of earthquakes based on the energy released.

Alfred Wegener (often misspelled as Wrenger in some texts) is the scientist credited with first proposing the theory of Continental Drift in the early 20th century.

The point of origin of an earthquake is the focus (or hypocenter), not the epicenter (which is the point on the surface directly above). Homoseismal lines connect places that experience earthquake shocks at the same time.

Both statements are scientifically observed phenomena. Tectonic stress changes can indeed affect pore pressure in deep strata, leading to fluctuations in oil flow from wells, which is sometimes used as a precursor indicator for earthquakes.

Abyssal plains are vast, flat, and smooth areas of the ocean floor. They are found between the continental rise and the mid-ocean ridges and cover a significant portion of the Earth's surface (roughly 40-50%).

The Pacific Ocean is surrounded by the Ring of Fire, where major tectonic plates meet. These plate boundaries are the primary source of the frequent seismic and volcanic activity observed along the Pacific margins.

The continental shelf is submerged (1) and its average depth is indeed about 100 fathoms (2). Statement 3 is incorrect as the Atlantic has a larger percentage of continental shelves. Statement 4 is incorrect because shelves are generally narrow where mountains are close to the coast.

As tsunamis enter shallow water, their speed decreases due to friction, and their energy is compressed into a smaller volume, causing the wave height to increase significantly. Statement 3 is incorrect because tsunamis are not just gentle rises and falls; they are powerful, destructive surges.

The Baltic Sea is a stable, shallow basin located on the Eurasian plate, far from active plate boundaries where volcanic activity typically occurs.

Tsunamis are generated by seismic activity (earthquakes), volcanic eruptions, or underwater landslides, not by tidal forces.

The ocean floor contains vast mountain ranges, deep trenches, and expansive plains that are far more varied and rugged than the topography found on land.

The Atlas Mountains are located in North-Western Africa. The other options are geographically incorrect (e.g., Abyssinian Plateau is in Ethiopia/East Africa, Guiana Highlands are in South America).

The point of origin inside the Earth is the focus (or hypocenter), not the epicenter (which is on the surface). Homoseismal lines join places affected at the same time.

Kolkata is in Zone IV, Guwahati is in Zone V, Delhi is in Zone IV, and Chennai is in Zone II. Matching these gives A-3, B-1, C-2, D-4.

All statements are correct: S-waves are shear waves, travel only through solids, are slower than P-waves, and have a speed roughly 60% of P-waves.

All statements are correct regarding the geologic time scale and orogenic phases: there are multiple phases, Alpine is the most recent, and the listed mountain ranges are correctly categorized by their respective orogenic periods.

Body waves travel through the interior (A-1). Surface waves are more destructive (B-2). P-waves are compressional (C-3). S-waves are transverse (D-4).

Fold mountains are formed by tectonic compression, block mountains are formed by faulting, volcanic mountains are formed by accumulation of materials, and residual mountains are remnants of eroded plateaus like the Deccan.

Reunion Island is a volcanic island located in the Indian Ocean, formed by a hotspot. The others are either continental fragments or coral atolls.

Acid lava is high in silica content, making it highly viscous and prone to explosive eruptions due to trapped gases. Its high viscosity and slow flow often lead to the formation of steep-sided domes, spines, or plugs.

Carbonation is chemical weathering, corrasion is mechanical wear by tools, attrition is the wear of particles against each other, and hydraulic action is the physical force of water.

The Eucla Basin is a large sedimentary basin in Australia that underlies the Nullarbor Plain, a vast arid limestone region.

The Pamir Plateau, often called the Roof of the World, is generally considered the highest plateau, with an average elevation exceeding 4,000 meters.

Major earthquakes like the 2010 Chilean earthquake release immense energy that can subtly shift Earth's mass distribution, altering its axis of rotation, and can cause significant coastal uplift, raising islands by meters.

The Atlas Mountains are a mountain range in North-Western Africa, spanning Morocco, Algeria, and Tunisia.

All statements are correct: 'tsu' and 'nami' are Japanese, they are caused by seafloor deformation, they have long wavelengths, and can be caused by landslides or volcanic eruptions.

A rift valley is formed by the subsidence of a block of the Earth's crust between two parallel faults.

Mountain building, or orogeny, is a complex geological process. It involves plate tectonics, folding and faulting of rock layers, volcanic activity, and igneous intrusions, all of which contribute to the formation of mountain ranges.