Volcanoes/ Gunung Api

The Indonesian volcano Anak Krakatau erupts at night

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.
There are three common types of volcano: composite volcanoes, often the most deadly; shield volcanoes, which are large but generally less violent; and cinder cones.

Volcanoes

A volcano is an opening, or rupture, in a planet's surface or crust, which allows hot magma, volcanic ash and gases to escape from the magma chamber below the surface.

Volcanoes are generally found where tectonic plates are diverging or converging. A mid-oceanic ridge, for example the Mid-Atlantic Ridge, has examples of volcanoes caused by divergent tectonic plates pulling apart; the Pacific Ring of Fire has examples of volcanoes caused by convergent tectonic plates coming together. By contrast, volcanoes are usually not created where two tectonic plates slide past one another. Volcanoes can also form where there is stretching and thinning of the Earth's crust in the interiors of plates, e.g., in the East African Rift, the Wells Gray-Clearwater volcanic field and the 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.

Erupting volcanoes can pose many hazards, not only in the immediate vicinity of the eruption. 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 stratosphere. Historically, so-called volcanic winters have caused catastrophic famines.

A plaster cast of a Roman Vesuvius victim in Pompeii

 Mount Vesuvius, a composite volcano, erupted in AD79 and killed thousands of people in the Roman cities of Pompeii and Herculaneum.
Archaeologists have discovered hollows in the volcanic ash where the victims' bodies fell and eventually decayed. They have filled these cavities with plaster to see the outline of their final resting places.
For many years it was assumed that lava killed the people of Pompeii and Herculaneum, but volcanologists later discovered it was something far more deadly.

The next Vesuvius eruption could be devastating

 

 Experts warn that a future major eruption of the volcano could put resident's lives at risk. However, it cannot be predicted when Vesuvius will erupt again.