What is a flood basalts?

Answer 1

Basaltic magma (properly called mafic magma) forms in areas of the mantle where silica (SiO2) is low, but iron and magnesium is high. This usually and most famously occurs along spreading ridges, where oceanic crust is formed, but can occur anywhere -- including surface volcanoes, which can form flood basalts as we commonly know them.

Answer 2

Basalt lava flows are not very viscous (a measure of resistance to flow) and so can flow easily and quickly across great distances delivering great volumes of basaltic rock. Some of these extrusions covered huge areas of the Earth and there is still potential for an eruption of this kind to happen again. Basalt lava flows have covered over a million and a half square kilometers of Siberia called the Siberian Trapps. The 65 million year old Deccan Trapps in India, a source of wonderful zeolite specimens, may have originally been just as large and its eruptions may have contributed to the extinction event that killed off the dinosaurs. The Columbia River Basalt Group is another huge basalt flow that could be over 6,000 feet thick. It covers large areas of Washington, Oregon and Idaho. Its soils contribute to the healthy potato crop from this region. Recent historic basalt flows have occurred on Iceland. The mara (black areas) on the moon are made of basalt and probably formed from basalt lava flows. And as might be expected, there also are large basalt flows on Mars.