Volcanoes are ruptures in the Earth's crust that allow magma and gases to escape to the surface. They typically form at boundaries where tectonic plates meet. The Pacific Rim is heavily populated with volcanoes due to converging tectonic plates. Volcanic eruptions release gases like carbon dioxide, water vapor, and sulfur dioxide that can impact the climate by increasing albedo and causing acid rain. Major eruptions can even lead to volcanic winters that endanger global vegetation and potentially trigger ice ages. Supervolcanoes pose an extreme threat as their eruptions could cause mass extinction events.