Earth’s Materials and Systems – Tectonic Processes

In this article, we’ll learn about Earth’s materials and systems, and Tectonic processes. Let’s begin with an introduction.

Introduction

We know that our planet is the only one in the solar system that has an abundance of water; thus, it is often referred to as the ‘water planet.’

Water covers approximately 71% of the earth’s surface (3/5th of the Northern Hemisphere and 4/5th of the Southern Hemisphere).

Similar to continental landforms (valleys, canyons, volcanoes, mountain ranges, plains), oceans contain a variety of landforms.

Plate Tectonics and the Ocean Floor

Bathymetry, or the shape of the ocean floor, is largely the result of plate tectonics. The Earth’s outer rocky layer is made up of about a dozen large sections known as tectonic plates, which are arranged like a spherical jigsaw puzzle floating on top of the Earth’s hot flowing mantle.

Convection currents in the molten mantle cause the plates to move a few centimeters around the Earth each year. Many ocean floor features are formed as a result of interactions between these plates.

The shifting plates can collide (converge), diverge, or slide past (transform). When plates converge, one plate may move beneath the other, causing earthquakes, volcanoes, and deep ocean trenches.

Molten magma flows upward between plates where they diverge, forming mid-ocean ridges, underwater volcanoes, hydrothermal vents, and new ocean floor crust. Faults that connect two areas where plates are converging or diverging are known as transform boundaries. These continental boundaries typically form zig-zag patterns.

Features of the Ocean

Based on its physical conditions, the ocean can be divided into several categories. These are the categories derived from the land:

Intertidal or littoral – Areas located between high and low tide. Crabs, barnacles, muscles, and other plants and animals rely on this ecosystem.

Continental shelf – The area between low tide and the shelf’s edge.

Continental slope – A steep slope of the ocean bottom to the ocean floor.

Abyssal plane: The ‘bottom’ of the ocean, where it is relatively flat, is known as the abyssal plane.

Hadal zones: These are regions with deep trenches in the abyssal plane.

The science of topography is the study of landforms. When we talk about the topography of the ocean floor, we’re referring to the various shapes that the ocean floor can take.

Continental Margin

What kinds of topographic features would you include on a map of the seafloor if you were asked? Until recently, most people were unaware of the characteristics of the ocean floor. Modern oceanographic techniques, including satellite data, show that the topography of the ocean floor is as diverse as that of the continents.

The seafloor’s topography is bumpy and irregular, with many high mountains and deep depressions. The Marianas Trench, which is in the Pacific Ocean, is roughly 11 km deep.

The continental margin is the area where continents’ edges meet the ocean. It is made up of sediment-covered continental crust that eventually meets oceanic crust. Continental margins are the ocean’s shallowest areas.

Landforms in the Ocean (Submarine Relief)

Under the ocean, there are mountains, basins, plateaus, ridges, canyons, and trenches.

Submarine relief refers to the relief features found on the ocean floor.

The ocean basins are classified into four major groups. They are as follows:

1. Continental Shelf
2. Continental slope
3. Abyssal plains
4. The ocean deeps/submarine trenches

Continental Shelf

The continental shelf is the shallowest part of a continental margin that extends seaward from the shore.

Continental shelves range in width from 30 to 60 kilometers.

The continental shelf on the Pacific coast of the United States is only a few kilometers wide, whereas the continental shelf on the Atlantic coast is hundreds of kilometers wide.

The average depth of water above continental shelves is approximately 130 meters. Remember that during the last ice age, the sea level was approximately 130 m lower than it is now; thus, most of the world’s continental shelves must have been above sea level at the time. As a result, today’s coastlines are very different from what they were during the last ice age.

At the time, the Bering land bridge connected Siberia to North America, Great Britain to Europe, and a large landmass existed where the Bahamas are now only scattered islands.

When the Earth’s surface began to warm after the last ice age and the continental ice sheets melted, the sea gradually engulfed the continental shelves. Beaches and other coastal landforms from that era are now submerged and spread far beyond the current shoreline.

Commercially valuable fish now inhabit the continental shelves’ shallow, nutrient-rich waters.

Continental shelves are very important to human beings. They provide fish, minerals such as sand and gravel, and so on.

The shelves provide a significant portion of the world’s petroleum and natural gas.

On continental shelves, coral reefs are also common.

The presence of submarine canyons that extend to the continental slope is one of the most striking features of the continental shelf. These canyons are ‘steep-sided valleys’ cut into the seafloor.

They resemble the gorges found on the continents.

The underwater landslide is one of the causes of the submarine canyon’s formation.

Continental Slope

The seafloor drops rapidly beyond the continental shelves to depths of several kilometers, with slopes averaging nearly 100 m/km. These sloping areas are known as continental slopes.

The continental slope is the true edge of a continent, according to marine geologists, because it generally marks the edge of the continental crust. This slope is cut by deep submarine canyons in many places. Submarine canyons are similar to land canyons, and some are larger than the Grand Canyon in Arizona.

Turbidity currents, which are rapidly flowing water currents along the seafloor that carry heavy loads of sediments, cut these submarine canyons, similar to mudflows on land.

Turbidity currents may form as a result of underwater landslides on the continental slope triggered by earthquakes, or they may form as a result of sediment stirred up by large storm waves on the continental shelf. Turbidity currents can travel at speeds of up to 30 km/h, effectively eroding bottom sediments and bedrock.

There is also far less sea life here than on the shelf.

Sediment deposits will form at the base of the continental slope. The continental rise is formed by this belt of sedimentary deposits.

Continental Rise

A continental rise is the gently sloping accumulation of deposits from turbidity currents that form at the base of the continental slope. A continental rise can have a thickness of several kilometers. The rise gradually thins out and eventually merges with seafloor sediments beyond the continental margin.

The continental slope ends in deeper depressions on the seafloor, known as deep-sea trenches, in some places, particularly around the Pacific Ocean. There is no continental rise at the foot of the continental margin in such places.

Deep-Ocean Basins

Beyond the continental margin are ocean basins, which cover approximately 60% of the Earth’s surface and contain some of the most interesting topography on the planet.

The Abyssal Plains

Abyssal plains are the flattest parts of the ocean floor, 5 or 6 km below sea level. Abyssal plains are plains covered by hundreds of meters of fine-grained muddy sediments and sedimentary rocks deposited on top of basaltic volcanic rocks.

The Abyssal Plains have Two Types of Relief Features.

1. Submarine Ridges are ocean mountains found near the middle of the ocean. submarine ridges are also known as mid-oceanic ridges. Volcanoes and earthquakes are common. The Mid-Atlantic Ridge is the world’s longest submerged mountain ridge.
2. Seamounts and guyots: Submerged volcanoes with sharp tops are known as seamounts and guyots. Guyots or table mounts are seamounts with a flattened top.

Deep Sea Trenches (Trenches in the sea):

The deep-sea trenches, which are elongated, sometimes arc-shaped depressions in the seafloor several kilometers deeper than the adjacent abyssal plains, are the deepest parts of the ocean basins. Many deep-sea trenches are found near volcanic island chains, such as Alaska’s Aleutian Islands, and the majority of them are found near the Pacific Ocean’s margins.

Deep-sea trenches are relatively narrow, measuring about 100 kilometers wide, but they can stretch for thousands of kilometers. The Peru-Chile trench, depicted in the figure below, is nearly 6000 km long and 40 km wide on average. The Mariana Trench in the Pacific Ocean is the world’s deepest known location.

Mid-Ocean Ridges

The mid-ocean ridges, which run through all of the ocean basins and have a total length of more than 65,000 km — a distance greater than the circumference of the Earth — are the most visible features of the ocean basins.

The average height of mid-ocean ridges is 1500 meters, but they can span thousands of kilometers. The tallest peaks in mid-ocean ridges rise above the ocean as volcanic islands.

Volcanic eruptions and earthquakes are common on mid-ocean ridges. These ridges’ crests frequently have valleys called rifts running through their centers. Rifts can reach depths of up to 2 km.

Ridges in the middle of the ocean do not form continuous lines. They are divided into shorter, stepped sections that run at right angles across each mid-ocean ridge. The areas where these breaks occur are referred to as fracture zones, as illustrated in figure 13 . Fracture zones are about 60 km wide and stretch for thousands of kilometers across the seafloor.

Hydrothermal Vents

A hydrothermal vent is a hole in the seafloor that allows magma-heated fluid to erupt. The majority of hydrothermal vents are found at the bottom of rifts in mid-ocean ridges.

When metal oxides and sulfides are present in the heated fluid erupting from these vents, they immediately precipitate out of the fluid and form thick, black smoke-like plumes. A black smoker is a type of hydrothermal vent that ejects superheated water at temperatures of up to 350°C. The black smokers were discovered in a rift valley of a mid-ocean ridge.

Warm water is emitted by the second type of vent, known as a white smoker. Seawater circulating through hot crustal rocks in the centers of midocean ridges causes smokers. Plate tectonics is the primary cause of mid-ocean ridges and the volcanic activity associated with them.