INTRO: Shield volcanoes are fascinating geological formations characterized by their broad bases and gentle slopes. Unlike their more explosive counterparts, these volcanoes are predominantly formed from fluid basaltic lava that flows easily across the landscape, creating their distinctive shapes. In this article, we will explore ten intriguing facts about shield volcanoes that highlight their unique features, formation, and significance in the study of volcanology.
Shield Volcanoes Feature Gentle Slopes and Broad Bases
One of the defining characteristics of shield volcanoes is their gentle slope, typically ranging from 2 to 10 degrees. This gradual incline is a result of the low-viscosity basalt lava that flows easily and spreads over large areas, allowing the volcano to build up in a broad and shield-like manner. The wide base is a key factor in distinguishing shield volcanoes from other types of volcanoes, such as stratovolcanoes, which have steeper profiles due to their explosive eruptions and the accumulation of ash and debris. The gentle slopes of shield volcanoes enable them to cover extensive areas, sometimes extending hundreds of kilometers wide.
Mauna Loa is the Largest Shield Volcano on Earth
Mauna Loa, located in Hawaii, holds the title of the largest shield volcano on Earth, covering an area of approximately 5,271 square kilometers (2,035 square miles). It rises about 9,170 meters (30,085 feet) from its base on the ocean floor, making it one of the tallest mountains in the world when measured from base to summit. Mauna Loa has erupted 33 times since its first well-documented eruption in 1843, with its most recent eruption occurring in November 2022. This immense volcano is not only a geological wonder but also a vital part of the Hawaiian Islands’ ecosystem and culture.
Basalt Lava is the Primary Eruption Material of Shields
The primary material ejected during eruptions of shield volcanoes is basalt lava, which is characterized by its low viscosity and high temperature. This type of lava can flow over long distances, allowing it to create the gentle slopes typical of shield volcanoes. The basaltic composition results from the melting of the Earth’s mantle, which is rich in iron and magnesium. When basalt erupts, it can form extensive lava fields, pahoehoe (smooth, ropy lava), and aa (rough, jagged lava) flows, all of which contribute to the volcano’s sprawling shape and size.
Shield Volcanoes Erupt Less Explosively than Stratovolcanoes
Compared to stratovolcanoes, shield volcanoes are known for their relatively mild eruptions. The fluidity of basalt lava means that gas can escape easily during an eruption, reducing the potential for explosive activity. In contrast, stratovolcanoes, which often feature more viscous magma, can trap gases and result in violent eruptions that produce ash clouds and pyroclastic flows. This difference in eruptive behavior makes shield volcanoes less hazardous to nearby communities, although they can still pose risks through lava flows and localized eruptions.
They Form Mainly at Hotspots and Divergent Boundaries
Shield volcanoes primarily form at geological hotspots and divergent boundaries. Hotspots are stationary plumes of magma that rise from the Earth’s mantle, creating volcanoes as tectonic plates move over them. The Hawaiian Islands, including shield volcanoes like Mauna Loa and Kilauea, are prime examples of this process. Divergent boundaries, where tectonic plates are moving apart, also facilitate the formation of shield volcanoes, as magma can easily rise to the surface to fill the gap, such as seen in the Mid-Atlantic Ridge.
Famous Examples Include Hawaii’s Mauna Kea and Kilauea
In addition to Mauna Loa, other prominent shield volcanoes can be found in Hawaii, such as Mauna Kea and Kilauea. Mauna Kea is noted for its snow-capped summit, reaching over 4,207 meters (13,803 feet) above sea level, and is revered in Hawaiian culture as a sacred mountain. Kilauea, on the other hand, is one of the most active volcanoes in the world, with continuous eruptions since 1983 that have reshaped the landscape of the Big Island. These volcanoes not only contribute to Hawaii’s unique geography but also serve as critical sites for scientific research and monitoring.
Shield Volcanoes Can Cover Thousands of Square Kilometers
The expansive nature of shield volcanoes allows them to cover vast areas, sometimes spanning thousands of square kilometers. For instance, the Deccan Traps in India is one of the largest volcanic provinces on Earth, formed by extensive basalt lava flows from shield volcanoes during the late Cretaceous period. This coverage can lead to significant geological features, such as large lava plateaus and extensive lava fields, which are crucial for understanding the history of volcanic activity and its impact on the Earth’s surface.
Erosion Plays a Significant Role in Shaping Their Features
Despite their robust structures, shield volcanoes are not immune to the forces of erosion. Over time, weathering and erosion can significantly alter their features, leading to the formation of valleys, ridges, and other geological formations. The gentle slopes are particularly susceptible to erosion from rainfall, wind, and other environmental factors, which can reshape the landscape and reveal the underlying geology. Understanding these erosional processes is essential for geologists as they study the long-term evolution of volcanoes and the landscapes they create.
Lava Tubes Often Form Beneath Shield Volcano Surfaces
One of the intriguing features associated with shield volcanoes is the formation of lava tubes, which are underground channels formed by flowing lava. As lava flows from a volcano, the outer surface cools and solidifies while the molten lava continues to flow beneath. Once the eruption ceases and the lava drains away, these hollow tubes can be left behind. Many lava tubes can be found in Hawaii, including the famous Thurston Lava Tube, which provides a unique opportunity to explore the inner workings of a shield volcano and witness the aftermath of volcanic activity.
They Are Key to Understanding Volcanic Activity and Hazards
Studying shield volcanoes is essential for advancing our understanding of volcanic activity and associated hazards. Their relatively non-explosive eruptions provide valuable insights into the behavior of basaltic lava and the processes driving volcanic activity. Moreover, researchers monitor these volcanoes to assess potential hazards to nearby communities and ecosystems. Understanding the patterns of eruptions, lava flow dynamics, and the geological context of shield volcanoes allows scientists to develop hazard assessments and inform preparedness strategies for volcanic eruptions.
OUTRO: Shield volcanoes are remarkable geological formations that play a significant role in the Earth’s volcanic landscape. Their gentle slopes, broad bases, and unique eruption mechanisms set them apart from other types of volcanoes. By exploring the various aspects of shield volcanoes, we gain valuable insights into the processes that shape our planet and the natural hazards that arise from volcanic activity. Whether it’s through the majestic landscapes of Hawaii or the insights into eruption dynamics, shield volcanoes continue to captivate scientists and nature enthusiasts alike.