A volcano is only dangerous if there are people living nearby for whom it can be dangerous. The Mount Erebus in Antarctica, which has been constantly erupting since 1972, is therefore harmless. Furthermore, a volcano is more dangerous as it erupts more violently or explosively.
Around 50 volcanoes erupt every year. Most of them are of the basaltic type, which rarely causes major problems. That is because basaltic magma flows very evenly, and almost never flows faster than a human can run. According to measurements, the lava from Mauna Loa in Hawaii only reaches 16 kilometers per hour.
However, there are also eruptions of volcanoes with rhyolitic and andesitic magma. These types contain more silicon than the basaltic magma, which produces a tough, thick current. As a result, a kind of plug can arise in the volcano, which only disappears when the pressure has risen so high that the volcano erupts.
However, Magma is not the only factor to determine to what extent a volcano is dangerous. After an eruption, pyroclastic clouds of glowing ash can flow down the mountain at lightning speed. Such a cloud blotted out all life in Pompeii in the year 79.
Dangerous gases can also flow from the cracks in volcanoes. Volcano gases cause 3% of all volcano-related deaths. Finally, a deadly aslawine can arise from a fierce rain shower. In 1985 it cost 23,000 lives at Nevado del Ruiz, Colombia.
Magma determines volcano power
Volcanoes erupt when there is overpressure of magma in the room. The various types of magma determine the course and the danger of the eruption.
Shield volcanoes (A) consist of light-flowing basaltic magma with few gases, which flow from one central pipe. Eruptions are rarely dangerous.
Cinder cones (B) consist of volcanic rocks, embers, which are formed from gas-rich magma. When the pressure drops, gas escapes and the magma explodes.
Strato volcanoes (C) consist of a layer of ash / embers and lava. When the tough magma erupts, the explosion is followed by a lava flow.