Features of Earthquakes & Volcanoes | Geography for GCSE/IGCSE - Year 11 PDF Download

Main Features of Volcanoes

• A volcano forms when magma erupts onto the Earth's surface as lava through a vent in the Earth's crust.
• The magnitude of a volcanic eruption is gauged using the Volcanic Explosivity Index (VEI). The VEI scale, although open-ended, reached its historical peak at 8 during the Tambora eruption in 1815.
• All volcanoes share common characteristics, illustrated in the accompanying diagram.

• Volcano formations vary depending on the type of lava erupted.
• Composite (or strato-volcanoes) are characterized by steep sides and the eruption of viscous, sticky lava.
• These volcanoes tend to have more explosive eruptions and are formed from alternating layers of ash and lava.
• They typically form on convergent (destructive) plate boundaries.

Shield Volcanoes

• Gently sloping sides
• Runny/thin lava
• Less explosive - gentle eruptions
• Tend to form on divergent (constructive) plate boundaries or hot spots
• Frequent eruptions

Volcanic Activity

Volcanoes may be active, dormant, or extinct

• Active: The volcano has recently erupted and is likely to erupt again
• Dormant: Has erupted in the last 2000 years and may possibly erupt again
• Extinct: Shows no evidence of eruption in historic times and there is no evidence of a magma reservoir

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Features of Eruptions

Eruptions may include a range of features as shown in the table below:

Main Features of Earthquakes

• Earthquakes occur as a sudden and intense shaking of the ground.
• The main cause of earthquakes is the accumulation of pressure resulting from the movement of tectonic plates.
• The epicenter of an earthquake is the location on the Earth's surface directly above the focus point where the earthquake originates.
• The focus of an earthquake is the spot beneath the Earth's surface where the seismic activity commences.
• Earthquake intensity, or the amount of energy released, is quantified using the Moment Magnitude Scale, which has superseded the Richter scale.
• The impact of earthquakes is evaluated using the Mercalli Scale, which measures the destruction and effects of the quake.
•  Tectonic Plates:  These are large sections of the Earth's lithosphere that float on the semi-fluid asthenosphere below.
•  Epicenter:  The epicenter marks the surface point directly above where the earthquake originates.
•  Focus:  The focus is the underground point where the seismic energy release begins.
•  Magnitude:  This refers to the energy released during an earthquake, crucial for assessing its impact.
•  Moment Magnitude Scale:  A more accurate scale replacing the Richter scale for measuring earthquake magnitude.
•  Mercalli Scale:  A scale that evaluates earthquake effects based on observed damage and human responses.

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Earthquake sequence

The sequence of an earthquake remains consistent irrespective of the boundary at which it occurs:

• Tectonic plates may become lodged as they move.
• Pressure accumulates as the plates continue to attempt movement.
• Eventually, the plates suddenly dislodge, releasing the accumulated pressure as energy.
• The origin point of the earthquake is known as the focus.
• Directly above the focus on the Earth's surface lies the epicenter.
• The energy disperses through the Earth's crust in the form of waves, resulting in the earthquake.
• Human activities like drilling or mining can also trigger earthquakes.

Human activities like drilling into the Earth's crust or mining can also trigger earthquakes.