Earth's Geological Features: Landforms, Oceans, and Rocks

Earth's Geological Features

Continental Landforms

Mountain Ranges: Formation & Tectonics

Mountain ranges form through a slow process, taking about 100 million years, which is impossible to appreciate during a human lifetime.

The interaction of two tectonic plates is key to understanding mountain ranges. Areas where two plates *collide* are subjected to immense pressure, compressing sediments deposited on the ocean floor and causing them to fold, thus forming mountains. This explains why *volcanic and seismic movements* are frequent in mountainous regions.

Ocean Floor Topography

Key Seafloor Features

• Mid-Ocean Ridges: These are large underwater *elevations* located in the central part of the oceans. They have an average height of 2,000 meters and feature a central groove called a *rift*, where magma from the asthenosphere is deposited on *both sides*, creating new ocean floor.
• Oceanic Trenches: These are *submerged areas* that represent the greatest ocean depths. They form in subduction zones and are located along some volcanic islands and continental margins.
• Continental Shelves: This is the part of the continent covered by the sea, typically reaching a depth of about 200 meters.
• Abyssal Plains: These are vast, flat areas of the deep ocean floor, often reaching depths of up to 3,500 meters.
• Continental Slopes: These are steep slopes that descend from the continental shelf to the deep ocean floor.

Seafloor Dynamics: Creation & Destruction

The seafloor *crust* forms at mid-ocean ridges and is *destroyed* in oceanic trenches through subduction.

Rocks Originating from Earth's Interior

Endogenous Rocks: Magmatic & Metamorphic

Of the three main rock types, sedimentary rocks are formed by the action of external geological agents. However, most *magmatic* (igneous) and metamorphic rocks form within the Earth, and their origin is linked to the movement of tectonic plates. Both metamorphic and magmatic rocks are therefore called *endogenous*.

Igneous Rocks: Formation & Types

Igneous rocks are generated from the solidification of magma. As previously discussed, magma originates from within the Earth where the necessary conditions of pressure and temperature cause rock material to melt.

Mineral Composition & Cooling Rates

The mineral composition of igneous rocks is dominated by silicates. Due to their formation process, these minerals are often found crystallized. The amount and size of crystals depend on how the magma has cooled:

• If magma cools and solidifies slowly, *intrusive igneous rocks* (also known as *plutonic rocks*) form.
• If magma reaches the Earth's surface (either on a continent or under the sea), it solidifies quickly, forming *extrusive igneous rocks* (also known as *volcanic rocks*).

Intrusive (Plutonic) Igneous Rocks

Plutonic rocks *form* from magmas that solidify slowly inside the Earth.

They are composed of a set of strongly interlinked, crystallized minerals. They typically have no visible pores and exhibit a *granular* texture.

Examples include *granite* and *diorite*. The continental crust is primarily composed of granite.

Extrusive (Volcanic) Igneous Rocks

Volcanic rocks arise from the rapid cooling of magma that rises to the surface in the form of lava during a volcanic eruption.

If cooling occurs very rapidly, minerals have no time to crystallize, as seen in *obsidian* and *pumice*.