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A shield volcano is a type of volcano named for its low profile, resembling a shield lying on the ground. It is formed by the eruption of highly fluid (low viscosity ) lava , which travels farther and forms thinner flows than the more viscous lava erupted from a stratovolcano .
A shield is a large area of exposed Precambrian crystalline igneous and high-grade metamorphic rocks that form tectonically stable areas. [1] These rocks are older than 570 million years and sometimes date back to around 2 to 3.5 billion years.
The volcanic field covers an area of 1500 km 2, overlying Precambrian metamorphic and plutonic rocks of the Tuareg shield. Many cones are breached, and the dominantly basaltic and basanitic volcanic products are rich in peridotite and pyroxenite xenoliths and megacrysts. The youngest volcanoes rest on Neolithic terraces and are of Holocene age.
This list of shield volcanoes includes active, dormant and extinct shield volcanoes. Shield volcanoes are one of the three types [ specify ] of volcanoes. They have a short cone shape, and have basaltic lava which means the lava has low viscosity (viscosity is a measure of the ability for a liquid to flow)
The most important types of volcanic mountain are composite cones or stratovolcanoes and shield volcanoes. [10] [11] A shield volcano has a gently sloping cone because of the low viscosity of the emitted material, primarily basalt. Mauna Loa is the classic example, with a slope of 4°-6°.
[75] [27] The central shield volcano is the oldest, built mostly from 22 to 18 Ma but with a later phase from 17.5 to 13 Ma. The southern shield volcano formed from 21 to 14 Ma. The northern shield volcano was built mainly from 17 to 12 Ma. [76] These shield volcanoes erupted mostly basaltic and trachybasaltic lava flows. [27]
The Mount Edziza volcanic complex is a linear group of volcanoes in northwestern British Columbia, Canada. [8] [9] It is about 65 kilometres (40 miles) long and 20 kilometres (12 miles) wide, consisting of several stratovolcanoes, shield volcanoes, subglacial volcanoes, lava domes and cinder cones.
Iceland is a 1 km high, 450x300 km basaltic shield on the mid-ocean ridge in the northeast Atlantic Ocean. It comprises over 100 active or extinct volcanoes and has been extensively studied by Earth scientists for several decades. Iceland must be understood in the context of the broader structure and tectonic history of the northeast Atlantic.