Volcanoes are dramatic evidence of the powerful forces at work inside the Earth. Eruptions of ash, gas and lava destroy entire cities and kill large numbers of people.
Volcanoes also add nutrients to soils, creating perfect conditions for many crops. Some types of volcano make new sections of the tectonic plates that make up the surface of the Earth. Without volcanoes and our planet's plates, the dry land we live on would not be renewed, and weathering and erosion by water, wind and ice would eventually carry it all into the oceans leaving Earth a water world.
Image: The Indonesian volcano Anak Krakatau erupts at night (credit: Getty Images/Tom Pfeiffer/VolcanoDiscovery)
Aerials of Africa's lowest land point and time-lapse of its most active volcano, Erta Ale.
Wearing gas masks to protect against constant noxious fumes, the crew endured blistering day temperatures of more than 40 degrees. To capture an unusual perspective on this extremely hostile environment, the camera was extended out above the springs on a Jimmy Jib crane. The ever-moving lava lake at Erta Ale was recorded at night using 35mm time-lapse.
Volcanic activity breathes life into a barren void deep underwater.
he crew was sceptical about reports of colourful communities on these sea mounts, but 1.5km down the combination of a rocky volcanic substrate with a nutrient-rich current leads to a profusion of life. Red is virtually invisible in deep sea, so these extraordinary gardens of red gorgonians and orange sponges are effectively camouflaged.
Evidence of the world's biggest ever eruption lies in the Siberian Traps.
The Siberian Traps are the remnants of huge volcanic eruptions - flood basalt eruptions - that can last for millions of years and may have contributed to the devastating Permian mass extinction. This programme was first shown in 2002.
Our planet develops its inner heat.
Dr Iain Stewart explains how the Earth developed its inner heat during a time known as the Hadean eon, about 4.5 billion years ago.
Volcanoes may have played an important role in the emergence of life.
Dr Iain Stewart explains how volcanic activity on the early Earth may have played an important role in the emergence of life about four billion years ago. He visits hot springs in Rotorua, New Zealand, to meet Dr Bruce Mountain, who explains the theory.
A volcano is a rupture in the crust of a planetary-mass object, such as Earth, that allows hot lava, volcanic ash, and gases to escape from a magma chamber below the surface.
Earth's volcanoes occur because its crust is broken into 17 major, rigid tectonic plates that float on a hotter, softer layer in its mantle. Therefore, on Earth, volcanoes are generally found where tectonic plates are diverging or converging. For example, a mid-oceanic ridge, such as the Mid-Atlantic Ridge, has volcanoes caused by divergent tectonic plates pulling apart; the Pacific Ring of Fire has volcanoes caused by convergent tectonic plates coming together. Volcanoes can also form where there is stretching and thinning of the crust's interior plates, e.g., in the East African Rift and the Wells Gray-Clearwater volcanic field and Rio Grande Rift in North America. This type of volcanism falls under the umbrella of "plate hypothesis" volcanism. Volcanism away from plate boundaries has also been explained as mantle plumes. These so-called "hotspots", for example Hawaii, are postulated to arise from upwelling diapirs with magma from the core–mantle boundary, 3,000 km deep in the Earth. Volcanoes are usually not created where two tectonic plates slide past one another.
Erupting volcanoes can pose many hazards, not only in the immediate vicinity of the eruption. One such hazard is that volcanic ash can be a threat to aircraft, in particular those with jet engines where ash particles can be melted by the high operating temperature; the melted particles then adhere to the turbine blades and alter their shape, disrupting the operation of the turbine. Large eruptions can affect temperature as ash and droplets of sulfuric acid obscure the sun and cool the Earth's lower atmosphere (or troposphere); however, they also absorb heat radiated up from the Earth, thereby warming the upper atmosphere (or stratosphere). Historically, so-called volcanic winters have caused catastrophic famines.