Why do shield volcanoes have broad, gentle slopes?
Quick Answer
Their lava is very fluid, so it spreads far before cooling. Repeated thin flows build a wide, low-profile mountain instead of a steep cone.
The Full Story
Shield volcanoes are usually built from basaltic lava that is hot and low in silica, making it runny. Because the lava can travel long distances, it piles up in thin layers over a broad area rather than stacking steeply. This creates the huge, gently sloping shape seen at volcanoes like Mauna Loa and Kīlauea in Hawaii. Eruptions are often effusive rather than explosive, although gas-rich episodes can still be dangerous. Over time, many eruptions produce a massive volcanic edifice wider than it is tall.
Key Facts
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