What are shield volcanoes?

Introduction

A shield volcano is a type of volcano. They are so named because of their shape which resembles a shield lying on the ground. Shield volcanoes are found wherever fluid, low silica lava reaches the surface of a rocky planet.

What are shield volcanoes?

Shield volcanoes are known as Hawaiian volcanoes. In this type, large quantities of extremely fluid magma are expelled without the explosive liberation of gasses or eviction or ejection of the pyroclastic materials. Lava flows out of a fissure or a central vent forming a shield. It has the appearance of a broad-domed shield.

Characteristics of shield volcano

• They have a broad and gentle slope, which resembles a warrior’s shield.

• Basaltic magma is the main component of shield volcanoes.

• They are non-explosive while erupting and give low gas content in lava.

• Lava moves slowly after the eruption of shield volcanoes.

• They vary in size, with some shield volcanoes being quite massive.

• Shield volcanoes can be active for long periods and may have frequent eruptions.

Stages of shield volcano

There are typically four stages that shield volcanoes go through.

1. Pre-Shield

The shield volcano starts with low volume and infrequent eruptions in the first stage.

2. Shield

In the second stage, the volcano accumulates 95% of its mass through continuous eruptions.

3. Post Shield

The eruptions become slightly more explosive in the third stage.

4. Rejuvenation

The shield volcano becomes active once again in the last stage by erupting small volumes of lava infrequently. If this stage does not proceed, then the shield volcano will erode slowly over time (1).

Parts of a shield volcano

A volcano’s essential components are

• Magma: Molten rock that exists below the surface of the earth is known as magma.
• Parasite cone: A miniature cone-shaped volcano created by the buildup of volcanic ash.
• Sill: A flat slab of rock created as magma solidifies in a volcano’s neck.
• Lava: Volcanic eruption of molten rock, solidifies as it cools.
• Flank: The side of a shield volcano.
• Crater: a volcanic vent is surrounded by a crater or the volcano’s mouth.
• Summit:- it is the highest point of the volcano.
• Ash:- smaller than 2mm-sized lava or rock fragments that are ejected into the air during volcanic eruptions.

Examples of shield volcano

There are just a few examples of shield volcanoes around the world.

• Mauna Loa, Hawaii, USA – One of the largest active shield volcanoes on earth.

• Kilauea, Hawaii – Another massive shield volcano located on the big island of Hawaii.

• Mauna Kea, Hawaii, USA – It is not as active as other volcanoes.

• Erta Ale – It is another active basaltic shield volcano located in the Afar Region of Ethiopia.

• Piton de la Fournaise, Reunion Island – An active shield volcano located in the western Indian Ocean.

The world’s largest shield volcano

Mauna Loa is the earth’s largest active shield volcano. Its summit rises 13,678 feet above sea level. It is located on the island of Hawaii in the U.S state of Hawaii in the Pacific Ocean.

Types of lava of shield volcano

Three main types of basaltic lava come out of shield volcanoes.

1. Pahoehoe lava

• This type of lava has a smooth surface and often looks like a twisted rope. 
• When the outer layer of a lava flow cools and solidifies, the molten lava underneath continues to flow. That is how pahoehoe lava gets created. 
• They are found on the upper slopes of shield volcanoes and travel long distances before solidifying.

2. Aa lava

• This type of lava has a rough, crooked surface and looks like a pile of broken rocks.
• It forms when the outer layer of flowing lava solidifies, but the molten lava underneath remains active.
• They are found on the lower slopes of shield volcanoes, and move slowly, therefore solidifying quickly.

3. Pillow lava

• They are mound-like tubular, nearly spherical, or pillow-shaped structures associated mainly with underwater basaltic volcanism.
• When molten basaltic lava erupts from an underwater volcanic vent, it encounters cold water, causing the outer surface of the lava flow to cool and solidify quickly (2).

Q&A

• What is a shield-type volcano?

Shield volcanoes are usually constructed entirely of basaltic lava flows. They are dome-shaped and generally have gentle slopes.

• What are the 5 facts about shield volcanoes?

Five interesting facts about shield volcanoes are

• They are characterized by low profiles with 4-6 degrees slopes.
• Hawaii’s volcanoes like Kilauea, and Mauna Loa, are examples of shield volcanoes.
• Eruptions from shield volcanoes tend to be non-explosive due to the low viscosity of the basaltic lava.
• The broad slopes of shield volcanoes are ideal for agriculture, though eruptions can still threaten nearby areas.
• The largest shield volcano is the Olympus Mons volcano on Mars. it is nearly three times taller than Mt. Everest.

• When did a shield volcano last erupt?

Kilauea located on the Hawaiian islands, USA, is one of the most active volcanoes on the earth. It last erupted from September 10 to 16,2023.

• Is the shield volcano safe?

They are generally safe because pyroclastic materials do not come out during lava eruptions, making them safe compared to other volcanoes like composite volcanoes.

Summary

• Volcanoes are openings or vents on the earth’s surface through which lava comes out from the magma chamber located under the earth’s surface.
• A shield volcano is a type of volcano that pours basaltic lava and forms a dome-shaped structure after cooling.
• Also known as Hawaiian-type volcanoes majorly are found in the Hawaiian islands of the USA.
• They have a broad and gentle slope, which typically resembles a warrior’s shield.
• Basaltic magma is the main component.
• There are four major stages for the formation of shield volcanoes pre-shield, shield, post-shield, and rejuvenation.
• Major shield volcanoes around the world are Mauna Loa, Hawaii, USA., Kilauea, Hawaii., Piton de la Fournaise, Reunion Island, etc.
• Different types of lava on shield volcanoes are pahoehoe aa and pillow lava, they are different from each other.

References

• D.S.Lal. Physical Geography. Sharda Pustak Bhavan, Allahabad. Chapter 5- Vulcanicity and Volcanoes, Page no- 45-62.

• D.R.Khullar.ISC Geography.Kalyani Publishers, Kolkata.Chapter 08-Volcanoes and earthquakes, Page no-120-149.

• Savindra Singh.Geomorphology.Pravalika Publications Allahabad.Chapter 12-Vulcanicity and landforms,Page no-200-215.

Written By: Ankita Gangopadhaya