Question

This image shows lava at a temperature of about \(1200^{\circ} \mathrm{C}\) erupting on the seafloor west of the Tonga trench. What name is given to lava flows like these that erupt underwater?

Short answer

The lava flows are called pillow lava.

Step-by-step solution

Understanding the Problem

Identify what is being asked in the problem: determining the name given to lava flows that erupt underwater.

Specific Characteristics of the Lava

Note that the lava mentioned is at a high temperature of about \(1200^{\circ} \mathrm{C}\) and erupts on the seafloor.

Define Lava Flow Context

Understand that the context of the eruption is underwater, which changes typical volcanic processes due to rapid cooling and interaction with water.

Identify Underwater Lava Flow Type

Learn that when lava erupts under the ocean, it cools rapidly due to the contact with water, forming distinct, rounded shapes. These flows are commonly known as "pillow lava."

Key concepts

Underwater Volcanic Eruptions

Underwater volcanic eruptions occur when magma from beneath the Earth's crust is expelled through volcanic vents on the ocean floor. These eruptions are similar to those on land but involve unique processes because of the surrounding water. Unlike on the surface, where magma cools slowly, underwater eruptions cause the hot lava to cool rapidly when it contacts cold seawater. This results in the formation of a distinct type of lava known as pillow lava.

• Rapid cooling in water leads to the creation of a solid crust, while the interior remains hot.
• The crust cracks as new lava gets extruded, forming a series of bulbous structures that resemble "pillows."

Most underwater eruptions occur along mid-ocean ridges, or at subduction zones, where tectonic plates collide or pull apart. These areas are hotspots for volcanic activity, where the Earth's mantle melts and creates magma. The rapid cooling and high pressure under the sea create unique geological features different from terrestrial volcanoes.

Seafloor Geology

Seafloor geology involves studying the structures and processes that shape the ocean bottom, a vast and largely hidden part of the Earth's crust. Many fascinating geological phenomena occur on the seafloor, including the formation of new crustal material and dynamic volcanic activities.
Underwater eruptions contribute to seafloor spreading, a process linked closely with the movement of tectonic plates. As magma rises and solidifies, it forms new seafloor crust, pushing the tectonic plates apart. This process continually renews and reshapes the ocean floor.

• Pillow lava is one of the distinctive geological structures found on the seafloor.
• Beyond volcanic formations, submarine ridges and hydrothermal vents are key landscape features.

These geological features are not just unique formations; they promote diverse ecosystems. Many marine species depend on the mineral-rich environments fostered by these volcanic activities.

Volcanic Processes

Volcanic processes govern how magma originates, moves, and finally erupts from volcanoes. These processes are central to understanding both terrestrial and submarine eruptions. In underwater settings, volcanic processes follow similar stages to those on land but are influenced significantly by the surrounding water.
The high-pressure and rapid cooling environment of the ocean floor lead to different behaviors compared to land eruptions.

• Magma under the ocean is less explosive because of sea pressure.
• Lava quickly cools and solidifies into pillow shapes rather than spreading like land lava flows.

The underwater volcanic processes are influenced by factors such as water depth and temperature. Hydrothermal circulation, where cold seawater percolates down through cracks in the seafloor, heats up, and then rises back to the ocean, is a vital process associated with underwater eruptions. This process not only cycles water but deposits minerals, providing essential nutrients for marine life and affecting global geological cycles.