Red volcanoes – effusive
Low gas content | High temperatures (1200ºC) | Fluid lava | Fast lava flows | Little ash | Poorly explosive eruptions
Grey volcanoes – explosive
High gas content | Lower temperatures (500-800ºC) | Visqous lava | Slow lava flows and domes/spines | Lots of ash | More explosive eruptions
Volcanic ash and lava flows can have a similar composition. The gas and silica contents in the magma is what creates a more or less explosive eruption. During an explosive eruption, the magma will be pulverized into tiny fragments: ash! Try with modeling clay: if you pull on it slowly, it bend, much like a lava flow. If you pull it brutally, it breaks like with ash in an explosion. Did you know ? Now you do!
If we go into detail, we define several types of volcanoes according to the type of activity and the power of the eruptions. For this purpose, scientists created a scale: Volcanic Explosivity Index (VEI)
The place of an eruption on this scale depends on the volume of the eruption and the height reached by the volcanic projections.
(Fortunately) the most explosive eruptions are the least frequent… For example a VEI 5 eruption, such as the one responsible for the destruction of Pompeii, on the slopes of Mount Vesuvius, only occurs statistically every few hundred years.
Therefore we define Hawaiian, Strombolian, Vulcanian, Plinian and Ultra-Plinian eruptions.You find it difficult to comprehend how high lava fountains or ash plumes get?
Follow the guide…
Lava fountains of Hawaiian-style eruptions can rise to the height of the Sagrada FamiliaBasilica (Barcelona, Spain).
Vulcanian eruptions can exceed easily 10 times the height of the Eiffel Tower.
The ash plume of a Plinian eruption reaches the height of Mount Everest without any problems! … And an ultra-Plinian doubles the height!!