When volcanic activity takes place above ground, so that hot molten magma is released onto the landscape, we say that the volcanic activity is extrusive, meaning it is on the exterior, or outside of the Earth. Magma that reaches the service is known as lava.
Lava flows are extraordinarily hot, and destructive. In many cases, these lava flows are slow and continuous, as is the case with the volcano on the Hawaiian Island. Hot lava flows year after year down the volcano, creating new terrain, rarely exploding.
In other cases, volcanoes can erupt with unbelievable force and power. These types of eruptions can send lava, rock, and hot ash, known as pyroclastic material shooting outward for hundreds of square miles, in some cases, even sending up a worldwide cloud of dust and ash.
One example of such an eruption is the island of Krakatua. In 1883 this island volcano exploded in a colossal event that completely destroyed the island, leaving nothing but ocean behind. The noise from the explosion was heard as far as 1,500 miles away, and dust filled the sky worldwide, creating beautiful sunsets for months.