The heat of volcanoes and hot springs comes from trace amounts of radioactive minerals found in the Earth's interior. Why isn't the same rock at the Earth's surface warm?

Answer 1

From Britannica Online:

Hot springs and geysers also are manifestations of volcanic activity. They result from the interaction of groundwater with magma or with solidified but still-hot igneous rocks at shallow depths.

Answer 2

A microwave oven has a power requirement of 1248 W. A frozen dinner requires 4.1 min to heat on full power. How much electrical energy (in kWh) is used?