What Are Shield Volcanoes?

What makes shield volcanoes different?

Shield volcanoes form from basaltic lava that is relatively low in silica and gas content. This thin, runny lava flows easily and travels long distances before cooling and solidifying. Over many eruptions, the accumulating flows build a broad, gently sloping mountain with slopes typically only 2-10 degrees, far less steep than stratovolcanoes (which can reach 30 degrees or more). The eruption style is also different: shield volcanoes tend to have relatively gentle, effusive eruptions rather than explosive ones, though they can still produce dramatic lava fountains and rivers.

How do shield volcanoes form?

Shield volcanoes typically form over hotspots, where deep mantle plumes deliver a steady supply of basaltic magma to the crust. The Hawaiian Islands all formed this way, as the Pacific Plate slowly moved over a stationary hotspot. They can also form along divergent boundaries like Iceland's volcanoes, which sit on the Mid-Atlantic Ridge where the North American and Eurasian plates pull apart. The frequent eruptions of fluid basaltic lava add layers continuously, building the wide gentle slopes characteristic of shield volcanoes over hundreds of thousands of years.

What are famous shield volcanoes?

Mauna Loa in Hawaii is the world's largest active volcano by volume, covering about half the island of Hawaii. Mauna Kea, also in Hawaii, is the tallest mountain on Earth from base to summit (over 33,000 feet from the ocean floor). Kilauea is the most active Hawaiian volcano, with continuous eruptions for decades at a time. Iceland has many shield volcanoes including Skjaldbreiður (which gave the name 'shield' to the type). The African shield volcanoes include Erta Ale in Ethiopia and Mount Nyiragongo in the Democratic Republic of the Congo.

How dangerous are shield volcanoes?

Shield volcanoes are generally less dangerous than explosive stratovolcanoes because their eruptions are usually gentler, with lava flowing rather than exploding. However, the lava itself can destroy anything in its path, including homes, roads, and entire communities. Kilauea's 2018 eruption destroyed over 700 homes in Hawaii. The slow-moving lava lets most people evacuate, but property damage can be total. Shield volcanoes also produce dangerous gas emissions (sulfur dioxide especially) that can harm health and crops over wide areas downwind.