Volcanic eruptions are a constant reminder that Earth is an ever-changing, sometime destructive force. Humans cannot alter geologic events to prevent eruptions from occurring. Instead, people must predict when eruptions will occur and what impact they will have on human population. Constant observation and knowledge about the effects of volcanic eruptions best prepare people to minimise casualties and losses from a volcanic event.
Volcanoes can reach very high elevations. As a result, the peaks of these tall volcanoes are likely to be covered by ice and snow. This may look aesthetically pleasing, but the ice and snow are actually serious hazards should the volcano begin to erupt. Once a volcanic eruption has taken place, the lava and hot gases melt the snow. Heated water will then rush down the side of the mountain picking up dirt and debris along the way.
Gases and fragments of the volcano are released during an eruption. Gravity pulls this plume of hot gas and rock fragments downward, along the sides of the volcano. This is known as a pyroclastic flow. A pyroclastic flow is one of the most dangerous effects of a volcanic eruption. These superheated gases and rock fragments make their way down the mountainside at speeds of up to 450mph and can flow outward for miles beyond the base of the volcano.
Volcanoes pose another threat when they are located next to bodies of water -- tsunamis. Eruptions can cause landslides or even cause entire sections of the volcano to collapse. Tons or rock and debris fall into water, displacing a massive amount of water in a short period of time. This is what generates tsunami waves. Underwater volcanic eruptions can have the same effect, where water is forced upward quickly, creating displacement waves. These tsunamis travel quickly and can be devastating to surrounding land.
Earthquakes are also a result of volcanic eruptions. Hot magma is injected into the surrounding rocks during an eruption. This movement of magma causes fluctuations in pressure, which can cause tremors. These kinds of earthquakes can be felt before, during and after the eruption takes place. Another way a volcanic eruption can cause an earthquake is the eruption expels magma and solid rock moves to fill in the void left behind. This movement causes an earthquake.