Facts about lava

14 lava facts

Molten rock released from inside the Earth

Lava is molten material from the Earth's interior (magma) that has escaped to the surface.

It is not identical to magma, its composition is slightly different.  It consists mainly of molten oxides of silicon, sodium, iron, potassium, calcium and other metals, and is free of volatile substances. The solidifying lava forms effusive magma rocks, the most common of which are basalt, trachyte, riolite, andesite, and obsidian or pumice.

Lava is molten or partially molten rock (magma) that has risen to the surface as a result of an eruption.

The hot, molten mass of silicates and aluminosilicates, mixed with oxides and sulfides, with large amounts of water and gases, formed lava as it rose to the surface.

Magma is formed in deep parts of the Earth's crust.

It is formed in the Earth's upper mantle, a layer of the crust that extends to a depth of about 400 kilometers and is characterized by considerable plasticity.

The upper liquid part of the upper mantle, just below the lithosphere, is called the asthenosphere (a layer about 250 to 300 kilometers thick). It can lie from 10 to 100 kilometers below the Earth's surface.

Magma is found not only under the Earth's surface.

It has also been found on other rocky planets (Mercury, Venus, Mars) and some natural satellites (moons).

Magma can also solidify deep within the Earth's crust.

It then forms intrusions, bodies of rock that have penetrated between older rock formations. In the shallower regions of the Earth's crust, magma rises in the form of diapirs (geological structures that take the form of chimneys, mushrooms, and walls) and pushes into the surrounding rocks.

Diapirs that reach close to the Earth's surface give rise to volcanic phenomena. However, most of these rocks, due to slow cooling, solidify 5 to 30 kilometers below the surface, forming rock bodies called plutons.

The temperature of lava, depending on its composition, can range from 700 to 1,200 °C.

Beyond Earth, lava can reach even higher temperatures; the record holder is Io, Jupiter's moon, where satellites have recorded lava flows with an average temperature of 1,300 °C (2,370 °F).

Magma can escape to the Earth's surface in the form of lava as a result of a volcanic eruption or through a fracture in the Earth's crust, both on land and underwater.

Lava is similar in composition to magma, but is depleted of volatile components. It consists mainly of molten oxides of silicon, iron, sodium, potassium, calcium, and other metals. 

Lavas are divided into three types based on their silicon dioxide (SiO2) content.

Lavas are distinguished by their acidity:

  • Acidic, which have a high silica content, are viscous, flow slowly (a few centimeters per hour), and solidify rapidly. Due to their relatively rapid solidification, they cause crater plugging, leading to violent eruptions.
  • Basic, which, due to their lower silica content, have a higher temperature (over 1,100°C), lower viscosity and are more mobile, so they flow faster and their spouts are quiet. With the right gradient, they can reach speeds of up to 50 km/h.
  • Intermediate, representing values between acidic and basic lava.
During a volcanic eruption, several hundred cubic meters of lava are usually ejected.

These volumes can vary, sometimes being very large, such as during the eruption of the Laki rift volcano in southern Iceland, where the volume was 12 km3. Volcanoes in Iceland, known as the land of fire and ice, can spew lava at a rate of 75 tons per second.

In 1783, the Skaptar volcano exploded in Iceland, destroying crops and food supplies across the island. Iceland was hit by a wave of famine that killed one-fifth of the island's population.

Lava can take many different forms.

Common forms are aa, pahoehoe and pillow lava.

One of the main types of flowing lava is "stony rough lava" - aa.

Aa is basaltic lava and is characterized by a rough, jagged surface. It forms rare but large gas bubbles which, as the lava solidifies during flow, promote its fracturing into large blocks. The temperature of this type of lava is usually between 1000 and 1100 °C (1830 and 2000 °F).

The name aa (ʻaʻā) was originally applied only to Hawaiian lavas. However, it has been adopted to refer to all lavas of this type. In Iceland this type of lava is called apalhraun.

The most common type of lava in Hawaii and Iceland is pahoehoe.

It is also known as "smooth, unbroken lava". It is characterized by low viscosity, a large amount of gas contained in small bubbles, and is usually basaltic in composition. As this type of lava cools, it forms a glassy coating as its exterior cools rapidly. Its interior, however, is still moving, causing the surface of the lava flow to wrinkle, resembling tightly bound strings. These are usually twisted and contorted, never forming a smooth surface.

Tunnels and caves formed within pahoehoe lavas are common.

Underwater eruption produces pillow lava.

It cools very quickly and splits into ellipsoidal, usually flattened lobes resembling pillows or loaves.

The individual pillows have a spongy structure in the center and a glassy structure on top, and are characterized by a concentric structure. The average size of a lobe is 30-60 cm, but they can also reach several meters.

Pumice is formed from acidic varieties of lava.

It is a volcanic magma rock composed of porous volcanic glaze (more than 50% pores), formed from highly gassy, frothy rhyolitic lava. Pumice is usually of a light, whitish color. 

The largest deposits of pumice are found in Armenia and the Aeolian Islands in the Tyrrhenian Sea.

Theoretically, magma can only be studied after it has become lava.

However, in situ magma has been encountered in geothermal drilling on three occasions - twice in Iceland and once in Hawaii.

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