ACTIVE VOLCANOES

Mt Etna is the largest active volcano in Europe. It has an elliptical base (38 x 47 km) and a maximum elevation of about 3350 m.
The volcano dominates the landscape of NE Sicily; Italy.Mt Etna has the longest period of documented eruptions in the world. Etna is noted for the wide variety of eruption styles. The volcano is at its most spectacular when both summit and flank eruptions occur simultaneously.
The structure of Mt Etna consists of a series of nested stratovolcanoes, characterized by summit calderas, the most important one being the Ellittico Caldera, which formed about 14,000-15,000 years ago. Historically Mt Etna has produced effusive activity; however several pyroclastic deposits related to Plinian eruptions have been identified in the Holocene sequence. Under open vent conditions, ash emission only occurs during flank eruptions of Mt Etna volcano.Structural and seismic data indicate that the regional deformation in the Etnean area is generally dominated by N-S compression as the result of subduction of the African tectonic plate under the Eurasian plate.

MINERALS IN EARTH CRUST

Earth's crust and mantle consist almost entirely of minerals, yet the number of known minerals is less than 3,000. Two factors limit the number of possible and actual minerals. First, a crystal's atoms must be arranged in some periodically repeating, three-dimensional pattern, but only a finite number of such patterns exist. Second, there are only a few score naturally occurring elements, many of which are rare and eight of which—oxygen, silicon, aluminum, iron, calcium, sodium, potassium, and magnesium, in order of decreasing commonness comprise 98.5% of Earth's crust by weight. Oxygen alone makes up approximately 47% of the crust by weight and silicon makes up approximately another 27%. The number of minerals that can form is therefore finite, and many of those that could theoretically form do so rarely.
The atoms of the two most common elements on earth, silicon and oxygen, readily arrange themselves into tetrahedra having a silicon atom at the center and an oxygen atom at each point. This unit is the silicate radical, (SiO4)4−. Silicate radicals can link into sheets, chains, or three-dimensional frameworks by sharing oxygen atoms. If every oxygen atom participates in two tetrahedra, then the overall ratio of silicon to oxygen is 1:2, and the resulting chemical formula is that of silica, SiO2. Minerals built mostly of silica are termed silicate minerals. The mineral quartz is pure crystalline silica; other silicate minerals result when atoms of elements other than silicon are introduced at regular intervals. For example, some of the tetrahedra in the silicate framework may be centered on aluminum atoms rather than silicon atoms. In this case, atoms of other elements (usually calcium, potassium, or barium) must be present to balance the ionic charges in the framework. The silicate minerals having this particular structure are the feldspars, which make up approximately 60% of the earth's crust by volume.

MINERALS IN IGNEOUS ROCKS

The mineral composition of igneous rocks contains mostly the elements oxygen and silicon, but many other elements form a variety of minerals in igneous rocks. There are three types of rocks, igneous, sedimentary and metamorphic. Igneous rocks form as a result of magma cooling and minerals within the magma crystallizing. There are a variety of minerals associated with igneous rocks and their abundance and crystal forms depend on the environment (pressure and temperature) under which the magma cooled. Igneous intrusive rocks crystallize very slowly as magma is pushed through the Earth's crust. Igneous extrusive rocks crystallize rapidly as magma is erupted through volcanic processes.

The Composition of Igneous Rocks:

Eight elements make up about 98 percent, by weight, of most magmas from which igneous rocks are made. These elements are:
• Oxygen (O)
• Silicon (Si)
• Aluminum (Al)
• Iron (Fe)
• Calcium (C)
• Sodium (Na)
• Potassium (K)
• Magnesium (Mg)
The composition of igneous rocks is mostly oxygen and silica. This is in agreement with the composition of the Earth's crust, which is also mostly oxygen and silica. Other elements that make up the remainder of igneous rock compositions include manganese (Mn) and Titanium (Ti).

COMPOSITION IN MOLTEN LAVA

Volcanic types are intricately connected with the types of magma, lava and volcanic rock (also known as igneous rocks) composition which shape the volcano and the surrounding area. Minerals form in igneous rocks when molten magma or lava solidifies. The densest minerals, ferromagnesian silicates, form at the highest temperatures, whereas less dense minerals form when the magma cools down. Mineral types forming in molten rock often grow unrestricted to a very large size, and can have a fine crystal form. At most basic, there are eight basic types of lava, which reflect the main types of volcanic rock which the lava is composed of. These types are:
• Basalt
• Andesite
• Dacite
• Rhyolite
• Carbonatite
• Natrocarbonatite
• Komatite

LAVA FROZEN UNDER SEA

For the first time scientists have mapped the layers of once molten rock that lie beneath the edges of the Atlantic Ocean and measure over eight miles thick in some locations. The research, reported in this week's edition of Nature, gives us a better understanding of what may have happened during the break up of continents to form new mid-ocean ridges. The same volcanic activity in the North Atlantic may also have caused the subsequent release of massive volumes of greenhouse gases which led to a spike in global temperatures 55 million years ago.
The scientists also developed a new method of seeing through the thick lava flows beneath the seafloor to the sediments and structures beneath. The technique is now being employed to further oil exploration of the area which was previously restricted by the inability to image through the lava flows. When a continent breaks apart, as Greenland and Northwest Europe did 55 million years ago, it is sometimes accompanied by a massive outburst of volcanic activity due to a 'hot spot' in the mantle that lies beneath the 55 mile thick outer skin of the earth.

Scientists mapped the huge quantities of molten rock in the North Atlantic. The rock had been injected into the crust of the earth at a depth of 5-10 miles beneath the surface along the line of the continental breakup 55 million years ago. Using seismic methods, they were able to map the layers of lava flows both near the surface and deep into the earth.

LAND UNDER OCEAN

The deep basins under the oceans are carpeted with lava that spewed from submarine volcanoes and solidified. At the dark bottom of our cool oceans, 85 percent of the earth's volcanic eruptions proceed virtually unnoticed. Though unseen, they are hardly insignificant. Submarine volcanoes generate the solid underpinnings of all the world's oceans massive slabs of rock seven kilometers thick.

Geophysicists first began to appreciate the smoldering origins of the land under the sea, known formally as ocean crust, in the early 1960s. Sonar surveys revealed that volcanoes form nearly continuous ridges that wind around the globe like seams on a baseball. Later, the same scientists strove to explain what fuels these erupting mountain ranges, called mid-ocean ridges. Basic theories suggest that because ocean crust pulls apart along the ridges, hot material deep within the earth's rocky interior must rise to fill the gap. But details of exactly where the lava originates and how it travels to the surface long remained a mystery.

MAGMA IN EARTH CRUST:

Magma is a mixture of molten rock, volatiles and solids, that is found beneath the surface of the Earth, and may also exist on other terrestrial planets. Besides molten rock, magma may also contain suspended crystals and gas bubbles. Magma often collects in magma chambers that may feed a volcano or turn into a pluton. Magma is capable of intrusion into adjacent rocks, extrusion onto the surface as lava, and explosive ejection as tephra to form pyroclastic rock.

Magma is a complex high-temperature fluid substance. Temperatures of most magmas are in the range 700 °C to 1300 °C (or 1300 °F to 2400 °F), but very rare carbonatite melts may be as cool as 600 °C, and komatiite melts may have been as hot as 1600 °C. Most are silicate mixtures.

Environments of magma formation and compositions are commonly correlated. Environments include subduction zones, continental rift zones, mid-oceanic ridges, and hotspots, some of which are interpreted as mantle plumes. Despite being found in such widespread locales, the bulk of the Earth's crust and mantle is not molten. Rather, most of the Earth takes the form of a rheid, a form of solid that can move or deform under pressure. Magma, as liquid, preferentially forms in high temperature, low pressure environments within several kilometers of the Earth's surface.

Magma compositions may evolve after formation by fractional crystallization, contamination, and magma mixing. By definition, all igneous rock is formed from magma.

While the study of magma has historically relied on observing magma in the form of lava outflows, magma has been encountered in situ three times during drilling projects—twice in Iceland, and once in Hawaii