8.10 Volcanic Landforms

Why is the Republic of Indonesia made of 17,508 islands?

Around the Pacific Rim is Indonesia, a nation built from the dotted volcanoes of an island arc. Indonesia is distinctive for its rich volcanic soil, tropical climate, tremendous biodiversity, and volcanoes. These volcanoes are in Java, Indonesia.

Landforms from Lava

Volcanoes and Vents

The most obvious landforms created by lava are volcanoes, most commonly as cinder cones, composite volcanoes, and shield volcanoes. Eruptions also take place through other types of vents, commonly from fissures (Figure below). The eruptions that created the entire ocean floor are essentially fissure eruptions.

Lava Domes

Viscous lava flows slowly. If there is not enough magma or enough pressure to create an explosive eruption, the magma may form a lava dome. Because it is so thick, the lava does not flow far from the vent. (Figure below).

Lava flows often make mounds right in the middle of craters at the top of volcanoes, as seen in the Figure below.

Lava Plateaus

A lava plateau forms when large amounts of fluid lava flow over an extensive area (Figure below). When the lava solidifies, it creates a large, flat surface of igneous rock.

Land

Lava creates new land as it solidifies on the coast or emerges from beneath the water (Figure below).

Over time the eruptions can create whole islands. The Hawaiian Islands are formed from shield volcano eruptions that have grown over the last 5 million years (Figure below).

Landforms from Magma

Magma intrusions can create landforms. Shiprock in New Mexico is the neck of an old volcano that has eroded away (Figure below). The volcanic neck is the remnant of the conduit the magma traveled up to feed an eruption.

Summary

• Landforms created by lava include volcanoes, domes, and plateaus.
• New land can be created by volcanic eruptions.
• Landforms created by magma include volcanic necks and domes.

Review

1. What is Shiprock and how did it form?
2. How do lava plateaus form?
3. What types of landforms are created by very viscous magma?

Explore More

Use this resource to answer the questions that follow.

1. How many separate eruptions created the basalts at Quincy, Washington?
2. How thick is the basalt?
3. When did the lavas begin to erupt?
4. How do scientists know that the Cascade volcanoes didn't erupt these lavas?
5. What type of volcanic vent did the eruptions come from?
6. What is the origin of all this volcanism?
7. How are the flows in eastern Washington different from those in Hawaii today?