One of the most destructive forces on Earth is also one of the most creative forces on Earth; volcanic eruption. When assessing the dangers of volcanic eruptions, it is best to divide those very real threats to two categories – primary or direct dangers, and secondary or indirect dangers.
When most people think of an eruption, the thoughts that come to mind regarding the dangers of this natural disaster are of the primary sort. That is, the explosive power itself is many times greater than that of an atomic blast. Huge rocks the size of houses can be hurled far into the air, to land many miles away from the volcano. Woe be it to the person standing anywhere near where such rocks land. Volcanoes produce many more smaller fragments, however, that are hurled even further, and in greater profusion, but which are every bit as deadly. These volcanic bombs, aptly named, are generally quite hot, and in any event, the force of even a small one is enough to cause as much damage to a human, animal, or structure as a cannonball.
Though not true of all the kinds of eruption, in an explosive eruption, an enormous amount of rock is pulverized to a fine dust or slightly larger fragments. Since this ash usually comes from the volcanic vents, it often is super heated and combines with super heated gas creating a Lahar or pyroclastic flow. Such flows are heavier than air, so the travel downhill at tremendous speeds, sweeping over and burying everything in their path. Most of the damage done in the well known eruption of Vesuvius in AD 79, that buried Pompeii was caused by these flows. The flooding that happened around the Mount St. Helens eruption was also caused by pyroclastic flows, when the intense temperature melted thousands of cubic meters of snow and ice.
In many cases, volcanoes produce enormous quantities of molten rock. This lava engulfs and incinerates everything in it’s path. This has been a common theme in places like Hawaii, and much of Oregon, Washington, and Idaho were primarily created by lava flows.
Then too, there are the gases. Whether hot or not, many of the gases released by a volcano are poisonous. Some can be smelled, such as various sulfides that may smell like rotten eggs, but some can be neither seen nor smelled, such as carbon dioxide. The amounts of these gases that are release in a single eruption is staggering; one volcanic eruption releases more carbon dioxide than all of mankind produces in an entire year. Carbon dioxide in high concentrations can kill by asphyxiation.
Secondary effects aren’t as often thought about. Sulfur dioxide will readily mix with water, creating sulfuric acid which can turn lakes, streams, and even rain, into death traps. The ash created by a major eruption will often circle the globe many times, and can (and has many times in recorded history) block sunlight, lowering the global temperatures. This can lead to crop failure and the resulting famine, and it may take years for the ash to clear from the atmosphere.
The ash itself is abrasive and very fine. When combined with water, as would happen when a person or other animal breaths it in, it creates a sort of cement, making respiration impossible.
As great as these dangers of volcanic eruptions are, and as horrendous as this natural disaster can be, there is still a good side. The land after an eruption is usually very fertile and will support crops that it may not have been able to before. Eruptions also very often create new land, particularly in areas near the sea. Scientists have even proposed that our oceans, and hence life on Earth, owe their existence to volcanic eruptions, that allowed water vapor to condense and fall as rain.
Rather than fearing eruptions, we should simply be aware of the dangers associated with them, and respect the power of mother Earth to both destroy, and to create. Only then are we able to weigh the benefits of living on the flanks of a volcano, against the dangers of being there, to make an informed choice.
