Just How Hot is Magma in the Earth?

Magma, the molten rock that lies beneath the surface of the earth, has a temperature that varies. Just how hot is magma? That answer depends on several factors. Magma reaches extreme temperatures, usually ranging from about 700 °C to 1,400 °C, or approximately 1,300 °F to 2,600 °F when it reaches the surface of the Earth. Depending on the type of rock and the pressure, magma can form at temperatures lower or higher than this range.

Where Does Magma Form?

The magma that typically reaches the surface of the Earth comes from depths of about 6 to 10 km, or 3.7 to 6.2 miles deep. That relatively narrow and shallow band, which lies from the lower portions of the crust to the upper part of the Earth’s mantle, feeds most known volcanoes. However, recent research shows that magma can form much deeper than that. Scientists now estimate that some magma can form at depths of 250 km below the Earth’s surface or more. That depth still lies fairly shallow in the mantle, which extends about 2,900 km, or 1,800 miles.

How Hot is Deep Magma?

Scientists can only estimate the temperatures of magma deep below the surface, at rifts beneath the ocean or in pools far below where they can take actual measurements. Various factors affect the temperature of deep magma, including the pressure at the depth where it lies, the type of rock it consists of, and the water content of the magma itself. Mantle plumes bring molten rock from deep within the Earth. The temperature of the magma in these plumes may be 1,600 °C, or about 2,900 °F or more.

What Type of Magma Is Hottest?

Scientists classify magma based on its chemical composition. The three general types of magma include basaltic, andesitic, and rhyolitic. These types of magma all contain mostly silicon dioxide, SiO₂, along with various other elements and compounds. Silicon dioxide, also known as silica, most often appears in nature as quartz, and is the major component of sand. The types of rocks that come from magma containing the most silicon dioxide are called felsic, and they are lighter in color than the mafic rocks that come from magma with a lower silicon dioxide content. In addition to varying compositions, each type of magma has a different temperature range as well.

Basaltic Magma

Basaltic magma contains approximately 45 to 55 percent silicon dioxide by weight. This type of magma includes compounds with high amounts of iron, magnesium, and calcium. It has low amounts of potassium and sodium. The average temperature of basaltic magma ranges from approximately 1000 °C to 1200 °C (1832 °F to 2192 °F). This range is the highest of the three most common forms of magma. When this type of magma cools, it often forms basalt, a fine-grained igneous rock often used in roads and other forms of concrete. If it cools slowly, it may also form diorite.

Andesitic Magma

Andesitic magma contains roughly 55 to 65 percent silicon dioxide by weight. This type of magma includes compounds with intermediate amounts of iron, magnesium, calcium, potassium, and sodium. The average temperature of andesitic magma ranges from about 800 °C to 1000 °C (1472 °F to 1832 °F). Andesitic magma can form an intermediate rock called andesite, which presents with a sort of mixed, salt and pepper appearance.

Rhyolitic Magma

Rhyolitic magma contains the highest amount of silicon dioxide of all three types, with approximately 65 to 75 percent by weight. This type of magma includes compounds with low amounts of iron, magnesium, and calcium, and high amounts of potassium and sodium. The average temperature of rhyolitic magma ranges from about 650 °C to 800 °C (1202°F to 1472 °F). This type of magma forms a highly viscous lava and often glassy rhyolite rocks, including obsidian and pumice.

Which Is Hotter, Lava or Magma?

Generally speaking, magma is hotter than lava. While magma remains below the Earth’s surface, it stays insulated by the surrounding rock. As it breeches the surface, and becomes lava, it begins to cool. Lava is still incredibly hot, but it may emerge from the face of the Earth as much as 200 °F cooler than the magma below.

Is Magma Hotter Than Fire?

As you have learned, magma is extremely hot. It can reach estimated temperatures of close to 1,600 °C, or about 2,900 °F. But depending on its source, fire can get much hotter. The temperatures of some wood fires can match the lower range of magma. However, these fires cannot approach the upper temperatures. Both coal and propane can burn at more than 1,900 °C, or about 3,500 °F, exceeding the upper estimates of magma. And acetylene burns at up to 2,200 °C, or about 4,000 °F, and when combined with oxygen up to 3,480 °C, or 6,300 °F. So, to answer this question, it depends on the fuel source whether magma is hotter than fire.

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