Why Do Shield Volcanoes Have Very Gently Sloping Sides?

Shield volcanoes are renowned for their gently sloping sides, a characteristic that makes them distinct from other volcanic formations like stratovolcanoes. This unique feature is mainly attributed to the specific eruptive and geological processes these volcanoes undergo. This article will explore the key reasons behind the gentle slopes of shield volcanoes, emphasizing the role of low viscosity lava, gentle eruptions, and geological settings.

Key Reasons for Gentle Slopes

Low Viscosity Lava

Shield volcanoes are predominantly filled with basaltic lava, a type of lava that is characterized by its low viscosity. This attribute is crucial in determining the shape and slope of the volcanic structure. High viscosity would restrict the flow of lava, making it thicker, more sluggish, and prone to forming steeper slopes. In contrast, low viscosity basaltic lava can travel further and spread over vast areas, creating the characteristic broad, gentle slopes.

Gentle Eruptions

Shield volcanoes are known for their gentle and non-explosive eruptions. These eruptions differ significantly from those of more explosive volcanoes like stratovolcanoes. Stratovolcanoes (also called composite volcanoes) often experience violent eruptions, which can produce steep and intricate formations. In shield volcanoes, the continuous flow of lava helps to spread out and cover large areas, maintaining a more gentle slope.

Layered Construction

The construction of shield volcanoes is layered and gradual. As lava flows repeatedly from the central vent, it builds up in broad, gentle layers, contributing to the shield shape. Each subsequent lava flow adds to the overall size of the volcano while maintaining a gentle slope. This process of repeated lava additions and gradual thickening results in the characteristic gentle slopes that make up the side of a shield volcano. Notable examples include Mauna Loa and Kilauea in Hawaii, where this layered construction process is clearly visible.

Geological Setting

The formation and maintenance of gentle slopes in shield volcanoes are also influenced by their geological location. Shield volcanoes are often found at hotspot locations or at divergent plate boundaries where tectonic activity is consistent and allows for a steady production of lava. This steady supply of lava contributes to the gradual accumulation of material, fostering the development of broad, gently sloping profiles.

In conclusion, the combination of low-viscosity lava, gentle eruptions, and layered construction results in the broad, gently sloping profile that is characteristic of shield volcanoes. These geological processes work together to create structures that are both visually striking and geologically fascinating, making shield volcanoes a pivotal subject in volcanic studies.

Further Reading:

USGS: Shield Volcanoes - Quiet Power Smithsonian Institution: Kilauea Volcano National Geographic: Mauna Loa Volcano, Hawaii

Note: Additional sources and further reading are provided for those interested in delving deeper into the subject matter.