C. Plate Tectonics (i) Name one tectonic plate on the Earth’s crust - Leaving Cert Geography - Question C - 2012

The area given to earthquakes and volcanoes that stretches around the Pacific Ocean is known as the "Pacific Ring of Fire." This region is characterized by frequent seismic activity due to the tectonic movements of the surrounding plates.

Volcanoes occur primarily through the movement of tectonic plates and the behavior of magma beneath the Earth's surface. Here is a detailed explanation of the process involved:

1. Magma Generation: Magma is formed in the Earth's mantle due to the melting of rocks under high temperatures and pressure. This occurs at subduction zones, where one plate is forced under another, as well as at divergent boundaries where plates move apart.

2. Magma Ascension: The less dense magma rises through the cracks and fissures in the Earth's crust. This ascension can create magma chambers beneath the volcano.

3. Pressure Build-Up: As more magma accumulates in the chamber, pressure builds up due to gases dissolved in the magma, such as water vapor and carbon dioxide.

4. Eruption: When the pressure exceeds the strength of the overlying rock, an eruption occurs. This can result in explosive eruptions, where ash and gases are expelled violently, or effusive eruptions, where lava flows gradually from the volcano.

5. Post-Eruption: After an eruption, the lava cools and solidifies, forming new rock layers. Over time, repeated eruptions can build up the structure of the volcano, leading to the formation of volcanic cones.

The interplay of tectonic movements, magma generation, and pressure dynamics are key to understanding how volcanoes form and erupt.