Question

What is the difference between magma and lava?

Short answer

Magma is molten rock beneath the Earth's surface; lava is magma that has erupted onto the surface.

Step-by-step solution

Understand Magma

Magma is molten or partially molten rock located beneath the Earth's surface. It is composed of a mixture of liquid rock, minerals, and dissolved gases. Magma can be found in the Earth's mantle and crust and is responsible for volcanic activity.

Identify Lava

When magma erupts from a volcano or through a vent in the Earth's crust and reaches the surface, it is referred to as lava. Lava is essentially the surface-exposed form of magma, and it cools and solidifies to form igneous rock.

Determine the Difference

The primary difference between magma and lava is their location relative to the Earth's surface. Magma is located beneath the surface, while lava is magma that has emerged above the surface.

Key concepts

Volcanic Activity

Volcanic activity is a fascinating natural process involving the movement of magma from beneath the Earth's surface.
When pressure builds up within the Earth's mantle, it can cause magma to rise up through the Earth's crust. The magma may emerge through volcanoes or vents, resulting in eruptions. During an eruption, not only does molten rock flow out, but gases and ash can also be released into the atmosphere.

• Volcanic eruptions can be explosive or effusive, depending on the composition of the magma.
• Explosive eruptions occur when gas-rich, viscous magma reaches the surface, often resulting in the violent release of ash and lava.
• Effusive eruptions happen when fluid basaltic lava flows out slowly, forming vast lava fields.

Once the magma reaches the surface and becomes lava, it begins to cool and solidify, contributing to the formation of different volcanic landscapes. Volcanic activity is crucial because it helps to shape the Earth's surface over geological time.

Igneous Rock Formation

Igneous rocks are formed through the cooling and solidification of magma or lava. The process of forming these rocks is directly related to volcanic activity. When magma cools slowly beneath the Earth's surface, it results in coarse-grained intrusive igneous rocks like granite. These rocks display clearly visible mineral crystals, thanks to the slow cooling process.

• Intrusive rocks: Formed slowly beneath the Earth’s surface.
• Extrusive rocks: Formed when lava cools rapidly on the Earth's surface.

In contrast, when lava cools quickly upon exposure to the atmosphere, it forms fine-grained extrusive igneous rocks like basalt. These rocks have minute crystals due to the rapid cooling rate. The mineral composition and crystal size of igneous rocks depend on the environment in which they cool.

Earth's Mantle

The Earth's mantle is an expansive layer located between the Earth's crust and its core. It is composed primarily of silicate rocks rich in iron and magnesium. The mantle is largely solid, but it harbors pockets of molten rock or magma, which are essential for volcanic activity.

• The mantle accounts for about 84% of Earth's total volume.
• Temperature and pressure increase with depth, influencing the movement of mantle material.
• Convection currents: These currents within the mantle facilitate the movement of tectonic plates.

The mantle plays a crucial role in tectonic activities and the earth’s thermal regulation. When mantle rocks partially melt, they generate magma, which may rise through the crust, contributing to volcanic eruptions.

Earth's Crust

The Earth's crust is the outermost layer of the planet, distinct from the mantle beneath it. This layer is relatively thin, composing less than 1% of Earth’s total volume. It is divided into oceanic crust, which is dense and mainly composed of basalt, and continental crust, which is less dense and comprises primarily granitic rocks.

• The crust varies in thickness between 5-70 kilometers.
• It is the surface layer on which all terrestrial life exists.
• The crust is broken into large pieces known as tectonic plates.

The crust serves as a fragile cover over the active mantle and is subject to movement due to tectonic forces. This movement can lead to earthquakes, volcanic eruptions, and the formation of mountain ranges. It is within the crust where magma either remains below as intrusive formations or breaches the surface as lava, continuing the cycle of magma-to-lava transition.