Answer
The eruptions that created the Columbia Plateau, such as those associated with the Columbia River Basalt Group, were characterized by extensive and widespread lava flows. These eruptions involved the release of vast quantities of basaltic lava through fissures and fissure vents, resulting in the formation of extensive lava plateaus. In contrast, eruptions that create large composite volcanoes, like Mount St. Helens, are typically more explosive and involve the ejection of pyroclastic materials, such as ash, pumice, and volcanic gases. These eruptions are often associated with the buildup of a large and steep-sided volcanic cone.
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