Violent and destructive, legendary in history and mythology, volcanoes in action are one of the most powerful forces of nature. They formed the Earth for billions of years and continue to do so, sometimes with fatal consequences for life and property.
An amazing witness, the erupting volcanoes are natural geological structures that provide a channel for the surface of the Earth to extrude molten rock materials that migrate from the depths to the earth's crust. Volcanoes can occur on land or on the seabed beneath the oceans.
Molten rock or magma, to use its proper geological name for a molten rock body found at depth, exists under pressure deep inside the Earth. When the imposition of solid rockets provides a channel, due to the constantly occurring internal adjustments of the surrounding rocks, magma can escape to move upwards in areas with lower pressure until they appear on the surface, acquiring a new name: lava. On the other hand, magma that cannot find a way out will be trapped forever in some kind of subsurface location.
Magma and lava are similar, but not the same. With a decrease in pressure on the ascending moving magma, most of the gaseous component is able to escape, thereby changing its composition. This modified molten rock will appear on the surface and then be called lava. In some cases, volcanic lava reaches the end of its ascending path with a volatile mixture of molten rock, gases and water, expanding and exploding with such force that the molten lava, fragments of rock and ash are forcibly moving into the air to great heights.
Active volcanoes emit carbon dioxide and other gases into the atmosphere, including significant amounts of water vapor. Volcanoes are not rare, and with tens of thousands of volcanoes erupting over hundreds of millions of years of the planet’s existence, the water vapor released by volcanoes provided a source of much of the Earth’s original oceans and much of its atmosphere.
Although the dramatic destruction scenes caused by volcanic eruptions capture our attention and imagination, volcanoes also created many advantages for young Earth. Volcanoes produce gases that escape from the atmosphere, and these gases contribute to the protective filtration of the harmful radiation of the sun. Volcanoes provide fertilizers for the soil — most of which come from volcanic eruptions, primarily they provide liquid in the form of water and nutrients and a habitat that helps make life possible. Volcanoes have created and still create the entire seabed of the oceans as a result of eruptions on the mid-ocean ridges, those mountain ranges that stretch across the globe, rising from the seabed. Most of the surface rocks and materials of the earth's crust are of volcanic origin. It is estimated that there are thousands of active volcanoes, as well as many inactive volcanoes that may re-awaken in the future. There are also many extinct volcanoes.
Volcanoes occur throughout the Earth, but many are concentrated on the edges of continents or benefit the sea, where they form underwater volcanic mountain ranges, or long chains of islands, such as Hawaii. A large number of active volcanoes surrounds the Pacific Ocean basin and has acquired the name “Pacific Ring of Fire”. There is a definite reason for this configuration over thousands of miles, and the explanation for this is due to the well-known geological theory known as Plate Tectonics, but this is too complicated to be discussed here. The same theory also explains the appearance of volcanoes on the edges of continents.
The form and structure achieved by volcanoes depend on the composition of the erupting lava and the amount of energy and power at their creation, and the main categories are somehow descriptive: conical cones, composite volcanoes, shield volcanoes and lava domes. The following is a brief description of these several types.
An example of a cone cone is Mexico’s famous Paricutin volcano, which suddenly, in 1943, began to grow from a farmer's field with explosive eruptions of molten lava into the air, forming ashes that fell to the Earth around the point of eruption. As this continued, the ash cone slowly formed until it reached a height of 1200 feet. Paricutin remained active for nine years, highlighting the ashes, which covered the surrounding area for many kilometers and destroyed the nearby city.
Composite volcanoes, as their name implies, are formed by the composition of alternating layers of hardened lava fragments and rock. Composite volcanoes are also called Strato volcanoes and reach a well-known high peak shape, sometimes covered with snow, as the often-depicted height of 12,400 feet of Mount Fuji, one of Japan’s sacred mountains. Other famous composite volcanoes are Vesuvius and Stromboli. There are several variants of the composite form.
Shield volcanoes are formed by lava, which flows easily and without the potential violence of some other forms. They are much flatter with wide areas at the highest level and sloping sides. Many of the largest volcanoes on Earth are shield volcanoes.
Probably the best example is the Hawaiian Islands, all of which are shield volcanoes, and the highest of these, measured from its base on the ocean floor, is Mauna Kea, 30,000 feet higher than Mount Everest. Hawaiian Islands are not like the Galactic Islands of the Pacific Ring of Fire, but they are called plume volcanoes. Molten material, which feeds plume volcanoes, occurs very deep in the Earth’s mantle, which is presumably located about 1,900 miles from the surface, much deeper than the source of magma for other types of volcanoes.
Lava domes are formed of very thick lava, which slowly flows with difficulty, cools and crystallizes before going far from its outlet, and is often compressed by more than one stream, forming lumpy pieces of hardened lava. Lava domes are often found in craters or on the sides of composite volcanoes.
Volcanic eruptions are most often remembered for the destruction they caused, and many eruptions have become particularly notorious. Almost everyone has heard of the Indonesian island of Krakatau, where in 1883 two thirds of the island disappeared with an explosion that was estimated to be 10,000 times more powerful than the atomic bomb explosion over Hiroshima at the end of World War II. A deadly tsunami followed this amazing event in Krakatau.
Another equally well-known event is the eruption in Italy of Mount Vesuvius in 79 AD, where the population of nearby Pompeii was overcrowded and buried almost immediately, so that it could be found and excavated later, becoming an appeal to historians and ordinary visitors .
Also in the Mediterranean, around 1600 BC, the island of Santorini and its civilization, now revealed by extensive archaeological excavations, were nearly destroyed as a result of the largest volcanic eruption in the last 10,000 years. It is believed that he killed more than a million people and destroyed the entire Minoan civilization on the island of Crete. Santorini may have also inspired Plato Island to Atlantis.
Other similar devastating eruptions were: Tambor, Indonesia, in 1815, after which 92,000 deaths occurred. The eruption of Mount Peli in the Caribbean in 1902 destroyed the city of St. Pierre and claimed the lives of all 29,000 prisoners, with the exception of one person who was imprisoned in an underground prison.
And in the recorded history there were dozens of other volcanic events that tell a similar story about the destruction and death of people.
And, of course, in the United States in 1980, in the state of Washington, the wonderful composite mountain of St. Helen lost about 1,200 feet of its summit in an impressive eruption, which was watched so many of us live on television.
And most recently in the United States, in Alaska, where there are many volcanoes, the Mount Redut volcano, which has been closely monitored for many months, finally erupted on March 22 of this year in 2009 against violence, which sent a massive cloud of volcanic ash up to 50,000 feet into the stratosphere. Undoubtedly, in the world there will be other similar eruptions.
Some volcanoes erupt explosively. One of these, mentioned above, refers to Mount St. Louis. Helen, when on May 18, 1980, one of the largest eruptions in the modern history of North America occurred. Not always erupting with such violence, volcanoes have played an important role in shaping the crust over time. Some extreme eruptions, known as “super-volcanoes,” in different prehistoric times millions of years ago created huge volumes of volcanic stone in vast areas in regions such as Yellowstone in the United States, Japan, the North Island of New York and Siberian traps and others. Huge volcanic events such as these are considered to be the main causes in several mass extinctions that occurred on Earth in four and a half billion years, including the widely known mass extinction event associated with the death of dinosaurs 65 million years ago.
