Earth Movements and Plate Tectonics

The Earth’s lithosphere, made up of rigid plates, is in constant motion due to the movement of molten magma beneath the surface. Let’s explore this fascinating phenomenon:

Earth’s Movement

Activity: Take a small colored paper pellet and place it in a beaker filled halfway with water. Heat the beaker on a tripod stand. As the water warms up, observe the movement of the paper pellet. You’ll notice that it moves upward along with the warm layers of water and then sinks back down along with the cooler layers of water. This activity mirrors the movement of molten magma inside the Earth.

Plate Tectonics:

• The lithosphere, which comprises the Earth’s crust and upper part of the mantle, is broken into several large and small rigid plates known as lithospheric plates.
• These plates move slowly, just a few millimeters each year, due to the circulation of molten magma underneath them.

Endogenic and Exogenic Forces:

• Earth movements are classified into two categories based on the forces that cause them:
  • Endogenic Forces: These are forces that act within the interior of the Earth.
  • Exogenic Forces: These are forces that act on the Earth’s surface.
• Endogenic forces cause both sudden and slow movements, such as earthquakes and diastrophic forces.
• Sudden movements like earthquakes and volcanic eruptions can cause significant destruction on the Earth’s surface.

Volcanoes

Volcano:

• A volcano is a vent or opening in the Earth’s crust through which molten material, such as lava, ash, and gases, erupts suddenly.
• The activity of volcanoes is a result of the movement of molten magma beneath the Earth’s surface.

Activity: Take a container, fill it with water, and close it with a lid. Put the water to boil. Now, put some peas, a spoon, and beads on top of the lid. Notice how the lid begins to shake as the water boils. The items on the lid also vibrate. This activity demonstrates how the Earth vibrates during an earthquake.

Earthquakes:

• Earthquakes occur when the lithospheric plates move. The vibrations generated by the movement of these plates are called earthquakes.
• The place in the Earth’s crust where the movement starts is called the focus, and the place on the surface above the focus is called the epicenter.

Types of Earthquake Waves:

• Earthquake waves include:
  • P waves or longitudinal waves
  • S waves or transverse waves
  • L waves or surface waves

Measuring Earthquakes:

• Earthquakes are measured using a machine called a seismograph, and their magnitude is measured on the Richter scale.

Earthquake Preparedness:

• During an earthquake, it’s essential to take shelter in safe spots such as under a kitchen counter, table, or desk, against an inside corner or wall.
• Avoid areas near fireplaces, chimneys, and windows that could shatter.
• Awareness and preparation can significantly reduce the impact of an earthquake.

Rivers and Coastal Landforms

Work of a River

Formation of Waterfalls:

• The running water in rivers erodes the landscape. When a river tumbles over very hard rocks or down a steep valley side, it forms a waterfall.

Formation of Meanders and Oxbow Lakes:

• As a river enters a plain, it twists and turns, forming large bends known as meanders. Continuous erosion and deposition along the sides of the meander cause the ends of the loop to come closer and closer. Eventually, the meander loop cuts off from the river, forming a cut-off lake, also called an oxbow lake.

Formation of Flood Plains:

• When rivers overflow their banks, they deposit layers of fine soil and other materials along their banks, forming flat, fertile floodplains. The raised banks are called levees.

Formation of Deltas:

• As the river approaches the sea, its speed decreases, and it begins to break up into a number of streams called distributaries. The river deposits its load, and each distributary forms its mouth. The collection of sediments from all the mouths forms a delta.

Work of Sea Waves

Coastal Landforms:

• The erosion and deposition by sea waves give rise to various coastal landforms.
• Sea waves continuously strike rocks, forming cracks that develop into hollow-like caves. Over time, these cavities become larger, forming sea caves. As these cavities grow, only the roof of the caves remains, forming sea arches. Further erosion breaks the roof, leaving behind wall-like features called stacks.
• A steep rocky coast rising almost vertically above the sea water is called a sea cliff.
• Sediments are deposited along the shores, forming beaches.

Work of Ice

Glacial Erosion and Deposition:

• Glaciers, often referred to as “rivers of ice,” erode the landscape by bulldozing soil and stones, exposing solid rock below.
• Glaciers carve out deep hollows, which fill up with water and become beautiful lakes in the mountains.
• The materials carried by glaciers, such as rocks, sand, and silt, get deposited, forming glacial moraines.