A volcanic eruption is caused by the movement of molten rock, known as magma, from beneath the Earth’s surface to the surface. When the magma is less dense than the surrounding solid rock, it rises towards the surface. As it ascends, gases dissolved in the magma expand due to the decrease in pressure. This expansion of gases increases the pressure within the magma chamber and pushes the magma through cracks in the Earth’s crust, resulting in a volcanic eruption.
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MCQs
1. What is found beneath the Earth’s surface that can cause a volcanic eruption?
A. Water
B. Magma
C. Sand
D. Oil
Answer: B. Magma
Explanation: Magma is molten rock beneath the Earth’s surface. When pressure builds up, it can cause a volcanic eruption as the magma seeks a way out.
2. What happens to the magma during a volcanic eruption?
A. It turns to ice
B. It becomes lava
C. It disappears
D. It turns to glass
Answer: B. It becomes lava
Explanation: When magma reaches the Earth’s surface during an eruption, it is called lava.
3. Which of the following can trigger a volcanic eruption?
A. Rain
B. Earthquake
C. Snow
D. Wind
Answer: B. Earthquake
Explanation: Earthquakes can shake the ground and crack the Earth’s crust, allowing magma to escape in the form of a volcanic eruption.
4. What role does gas play in volcanic eruptions?
A. It cools the lava
B. It increases pressure in the magma
C. It solidifies the magma
D. It absorbs the magma
Answer: B. It increases pressure in the magma
Explanation: Gases trapped in magma increase the pressure and can lead to explosive volcanic eruptions when released.
5. What is the name of the opening through which volcanic materials are expelled?
A. Crater
B. Cave
C. Pit
D. Tunnel
Answer: A. Crater
Explanation: A crater is the opening at the top of a volcano through which volcanic materials like lava, ash, and gases are expelled.
6. Which type of volcanic material can flow down the sides of a volcano during an eruption?
A. Rocks
B. Snow
C. Lava
D. Water
Answer: C) Lava
Explanation: Lava is the molten rock that flows out of a volcano during an eruption.
7. What is the term for a large volcanic explosion that can affect the global climate?
A. A lava flow
B. A volcano sprint
C. A volcanic winter
D. A magma storm
Answer: C. A volcanic winter
Explanation: The term for a large volcanic explosion that can affect the global climate is a “volcanic winter.”
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