Volcanic Hazards

With somewhere around 70 active and potentially active volcanoes to credit, the citizens of the United States are at a constant threat of volcanic hazards. Not many people out there seem to be concerned about these risks, and this is something which can be attributed to the widespread myths about volcanic eruptions. While most of these people believe that only those who live in the vicinity of a volcano are vulnerable to its hazards, the fact is that hazards like volcanic ash can also affect those who stay miles away from the site of eruption.

What are Volcanic Hazards?

With numerous instances of devastating volcanic eruptions in the history of our planet, there is no questioning the fact that volcanoes can cause widespread destruction in their surroundings. While the damage caused by other natural disasters - including earthquakes and hurricanes, can be repaired, the same cannot be said for the damage caused by a volcanic eruption. Discussed below are various hazards of volcanic eruption - right from harmful gases and landslides to lava flow and pyroclastic flows, that you cannot afford to turn a blind eye to.

Volcanic Gases
Magma, which lies beneath the Earth's crust, contains some dissolved gases which are released into the atmosphere during the volcanic activity. These gases are all the more hazardous as they can come out of those small cracks in the ground even when the volcano is not erupting. Water vapor happens to be the most abundant of these volcanic gases making up for 90 percent of the total release, followed by carbon dioxide, sulfur dioxide, etc., all of which are harmful for human health as well as the environment. While carbon dioxide, being a powerful greenhouse gas, adds to the near surface temperature of the planet by trapping radiations coming from the Sun, gases like sulfur dioxide react with droplets of water in the atmosphere and produce acid rain which is known to corrode metals and destroy the ecosystem of the planet.

Lahars
The term 'lahar' refers to the mixture of water - either hot or cold, and rock fragments that flow down the slopes of a volcano after a volcanic eruption. The size and velocity at which lahars travel can differ depending on the slope of the volcano and rock fragments water ratio. As with the lahar itself, even the rock fragments or debris that it contains vary in size. In the course of its journey downhill, a lahar can become 10 times its original size as more and more matter is eroded and added to it. Lahars are dangerous due to their tendency to cause economic as well as environmental damage as they bury human settlements, destroy agricultural land, bring down trees on their way, alter the course of the river etc.

Landslides
Though quite similar to a lahar, a 'volcanic landslide' or 'debris avalanche' is relatively smaller and has less water content as compared to it. As volcanic cones gain height owing to the ongoing volcanic activity, they tend to weaken from inside; and this weakened portion finally gives away after a point of time to cause a landslide. Other than an eruption, even heavy rainfall or an earthquake can trigger a volcano landslide. It does have the tendency to turn into a lahar though, but that can only happen if it gains huge mass and significant amount of water. Like lahars, even these landslides are known to cause a great deal of economic and environmental damage in the region.

Lava Flow
While lahars or landslides are no doubt devastating, even more devastating is 'lava flow' which doesn't just bury, but also burns everything that lies in its path. Lava flow can be triggered as a result of a non-explosive as well as an explosive type of volcanic eruption. The speed at which lava travels - i.e. flows, depends on the type of lava, its silica content (which in turn determines its viscosity), slope gradient, etc. Lava can destroy homes, agricultural land, cars, highways... basically anything that comes in its path by either burning it or burying it under several meters of lava which will eventually harden into a rock. It can also destroy water bodies such as rivers and lakes. As the speed at which the lava flows is relatively slow, deaths due to it are far less common - unless people are caught unprepared.

Pyroclastic Flows and Surges
Pyroclastic flows can be called a combination of all the aforementioned hazards of volcanic activity, though its severity is many times the severity of these hazards. Basically, pyroclastic flows are avalanches of highly dense rock fragments, volcanic ash and other gases which together travel down the volcanic slope at tremendous speed - at times exceeding 100 mph. While pyroclastic flows are common during explosive eruptions, the same can also occur when one side of the volcanic crater gives in to tremendous pressure that it is being subjected to. Also referred to as pyroclastic density current, pyroclastic lava can be as hot as 1,500°F, and that - along with its speed, makes it devastating for human property and environment alike. While pyroclastic flow tends to travel along the valleys, pyroclastic surges make their way over and beyond the ridges owing to the sheer amount of energy they have.

Tephra
The term tephra - which refers to lava and rock fragments that are blasted into the atmosphere, is most often associated with explosive volcanoes. Tephra fragments include minuscule particles - such as ash, as well as large rocks - referred to as bombs, with a diameter of one meter. When an eruption takes place, all these particles are propelled high into the air. While large rock fragments fall close to the vent, small rock fragments fall over a considerable distance. Similarly, volcanic ash - which forms an important constituent of tetra fragments, is carried away by the wind and deposited several miles away from the site of eruption. While hot rock fragments can damage structures or trigger fires in the surroundings, volcanic ash is known to cause respiratory problems and reduce visibility in the region. You get to hear several instances of volcanic ash bringing air traffic to a standstill in various parts of the world.

All these effects of volcanic eruptions give a rough idea as to how devastating a volcano can be, and how risky it is to reside in its vicinity. Our advancements in the field of science have been of some help as far as volcanic hazards mitigation is concerned. Several satellites are tracking the movements in the Earth's crust which cannot be traced by the naked eye, thus giving ample time for the authorities to take the necessary steps such as evacuation of people from a threatened region. However, we are yet to come to a point wherein we can accurately predict the eruption of a volcano or tackle its hazards, and until we do that we are left with no option but to live in constant fear of these hazards.