Question

Describe the activity in the mantle that leads to hot-spot eruptions. (D)

Short answer

Hot-spot eruptions occur when a plume of hot magma rises from deep within Earth's mantle to the crust, creating a localized region of volcanic activity that is not necessarily located along plate boundaries. The mantle's convection causes rock to melt, forming magma in these mantle plumes. As the less dense magma rises through the crust and erupts at the surface, a volcano is created. Tectonic plates above the hot-spot move, resulting in a series of volcanoes forming over millions of years. The activity in the mantle leading to hot-spot eruptions involves rock convection, magma formation from heated mantle rock, and magma rise through the Earth's crust, all culminating in volcanic eruptions.

Step-by-step solution

Define Hot-Spot Eruptions

Hot-spot eruptions refer to volcanic activity that occurs at 'hot-spots'. These are locations on the Earth's crust that are not necessarily located on plate boundaries. Volcanic activity here is the result of a plume of hot magma rising from deep within the Earth's mantle.

Describe the Earth's Mantle

The Earth's mantle is the layer beneath the crust and above the core. Though it is not molten, it is in a constant state of slow convection, meaning the solid rock moves as it heats up and cools down.

Explain the Origin of Magma

In certain regions, this convection causes the mantle rock to melt, forming magma. The heat that causes the rock to melt comes from the core of the Earth, and the area where this melting occurs is often referred to as a 'mantle plume'.

Describe Magma Rise Leading to Hot-Spot Eruptions

The magma formed in these mantle plumes is less dense than the surrounding rock. As a result, it rises through the mantle and the crust above it. When this rising magma reaches the surface of the Earth, it erupts, creating a volcano. These volcanoes can occur in the middle of tectonic plates—where the crust is normally stable.

Explain the Role of Tectonic Plates

As the tectonic plate above the hot-spot moves, the location of the eruptions changes. However, the mantle plume itself remains relatively stationary. This results in a series of volcanoes formed over millions of years, like the Hawaiian Islands for example.

Summarize the Mantle Activity Leading to Hot-Spot Eruptions

So, the activity in the mantle that leads to hot-spot eruptions involves the convection of solid rock, the formation of magma from heated mantle rock, and the rise of magma through the Earth's crust. This magma forms a volcano when it erupts at the Earth's surface. As the tectonic plate above the hot-spot drifts, new volcanoes can form, creating a chain of volcanic islands or mountains.

Key concepts

Mantle Convection

The Earth's mantle is an incredibly dynamic place, though it may not seem that way at first glance. Beneath the Earth's crust, the mantle is a thick layer composed of solid rock, yet it exhibits a fascinating process known as mantle convection. This process is akin to the way a pot of soup on a stove circulates as it heats up and cools down. It involves the slow movement of solid mantle rock due to the temperature differences between the hot inner core and the cooler outer parts of the mantle.

Warm, less dense material in the mantle rises towards the surface, while cooler, denser material sinks, creating a continuous cycle of movement. This movement may be slow, but it plays a significant role in the overall dynamics of our planet.

Understanding mantle convection helps to explain why certain regions of the mantle become heated enough to melt and form magma, which is crucial for phenomena like hot-spot eruptions.

Mantle Plumes

Mantle plumes are thermal anomalies within the Earth's mantle that have the ability to create hot-spot eruptions. These are essentially columns of hot, solid material that rise from the deeper parts of the mantle towards the crust. Imagine a narrow column of warm material pushing through a colder layer—this is similar to how a mantle plume operates.

As the plume ascends, it remains hotter than the surrounding mantle, which allows it to partially melt the rock it interacts with. This melting forms magma; since magma is less dense, it continues to rise through the Earth's lithosphere until it reaches the surface. Once it reaches the surface, it results in volcanic eruptions at places known as 'hot-spots'.

Unlike other types of volcanic activities that are directly associated with tectonic plate boundaries, hot-spot eruptions can occur in the middle of tectonic plates, thanks to these mantle plumes.

Tectonic Plates

Tectonic plates are massive slabs of the Earth's lithosphere that fit together like a jigsaw puzzle, forming the outer shell of our planet. They slowly but continually move, driven by mantle convection currents. This movement is what leads to seismic activities, such as earthquakes, and volcanic eruptions along plate boundaries.

However, when it comes to hot-spot eruptions, tectonic plates play a slightly different role. The mantle plume producing the eruption is relatively stationary, but the tectonic plate above it isn't. As this plate moves over the stationary hot-spot, it results in a chain of volcanic eruptions over time.

An excellent example of this phenomenon is the creation of the Hawaiian Islands, where the Pacific Plate has moved over a hot-spot, leading to a series of islands. This sequence demonstrates the influence of both mantle plumes and tectonic plate motion in shaping our planet's geology.