How are volcanic eruptions and earthquakes related to the Earth's composition and structure? Provide examples.

Volcanic eruptions and earthquakes are both related to the Earth's composition and structure in several ways.

1. Plate Tectonics: The Earth's crust is divided into several large and small pieces known as tectonic plates. These plates float on the semi-fluid layer of the mantle beneath them. The movement of these plates can cause both earthquakes and volcanic eruptions. For example, when two plates collide, one can be forced beneath the other in a process known as subduction. This can lead to the formation of volcanoes and earthquakes. The Pacific Ring of Fire, which includes countries like Japan, the Philippines, and New Zealand, is a prime example of this. It's an area with a lot of tectonic activity, leading to frequent earthquakes and numerous volcanoes.

2. Magma: The Earth's core is extremely hot, which heats the surrounding mantle, causing it to melt and form magma. When this magma rises to the surface, it can cause a volcanic eruption. For instance, the eruption of Mount St. Helens in 1980 was caused by a build-up of magma beneath the surface.

3. Fault Lines: Earthquakes often occur along fault lines, which are cracks in the Earth's crust where tectonic plates meet. When these plates move, they can cause the ground to shake, resulting in an earthquake. The San Andreas Fault in California is a well-known example of this. It's the boundary between the Pacific and North American plates, and its movement has caused many earthquakes.

4. Pressure and Heat: The Earth's structure is layered, with the most pressure and heat being in the core. This pressure and heat can cause the mantle to melt, forming magma. If this magma is forced upwards through the crust, it can cause a volcanic eruption. The 2010 eruption of Eyjafjallajökull in Iceland is an example of this.

In conclusion, the Earth's composition and structure play a significant role in the occurrence of both volcanic eruptions and earthquakes. The movement and interaction of tectonic plates, the formation and movement of magma, and the presence of fault lines all contribute to these natural disasters.