Lava is molten rock that erupts from a volcano during a volcanic eruption. When magma, which is found beneath the Earth's surface, rises and breaks through the crust, it becomes lava. This hot, liquid rock can flow down the sides of a volcano or spread out over the ground, cooling and solidifying into various types of rock. Lava can vary in temperature, composition, and viscosity, affecting how it flows. There are different types of lava, such as basaltic, which is low in viscosity and flows easily, and rhyolitic, which is thicker and more explosive. Understanding lava helps scientists study volcanic activity and its impact on the environment.