Important Questions: Our Changing Earth - Class 7 MCQ

• The location inside the Earth where an earthquake begins is called the focus (or hypocenter) of the earthquake.
• The point at the Earth's surface directly above the focus is called the epicenter of the earthquake.
• At the epicenter, the strongest shaking occurs during an earthquake.

A "vent" is associated with volcanic activity, where it refers to an opening in the Earth's surface through which volcanic material is emitted. The other options (fault, epicenter, and focus) are all related to earthquakes:

• Fault: A fracture in the Earth's crust where movement has occurred, causing an earthquake.
• Epicentre: The point on the Earth's surface directly above the earthquake's focus.
• Focus: The location within the Earth where the earthquake originates.

Erosion is wearing away of landscape by agents like water, wind, ice etc

• Fine particles of pulverized rock blown from an explosion vent. Measuring less than 1/10 inch in diameter, ash may be either solid or molten when first erupted.
• By far, the most common variety is vitric ash (glassy particles formed by gas bubbles bursting through liquid magma).

Wind is an active agent of erosion and deposition. In deserts we can see the rocks in the shape of mushroom due to the erosion of the lower part of the rock that is why mushroom rocks have wider top and narrower base.

When the wind blows, it lifts and transports sand from one place to another. When it stops blowing the sand falls and gets deposited in low hill – like structures. These are called sand dunes.

• Loess is an aeolian sediment formed by the accumulation of wind-blown silt, typically in the 20–50 micrometer size range, twenty percent or less clay and the balance equal parts sand and silt that are loosely cemented by calcium carbonate.
• Extensive loess deposits are found in northern China, the Great Plains of North America, central Europe, and parts of Russia and Kazakhstan.
• The thickest loess deposits are near the Missouri River in the U.S. state of Iowa and along the Yellow River in China.
• Loess accumulates, or builds up, at the edges of deserts.