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Why is Io one of the most volcanically active bodies in the solar system?

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Illustration showing the eight planets of the solar system in order from the Sun-Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune-depicted to scale by size, with labeled diameters in miles and kilometers. The Sun is partially visible on the left for comparison. — Solar system The planets (in comparative size) in order of distance from the Sun.

Io is the most volcanically active body in the solar system primarily due to intense tidal heating caused by its orbital environment.12

While radioactive decay is insufficient to power such extreme activity on a body of Io's size, the moon is caught in a gravitational tug-of-war. A gravitational resonance with the Jovian moon Europa forces Io into a slightly eccentric orbit. As Io orbits Jupiter, the planet's powerful gravitational field causes the moon to undergo continual flexing. This constant deformation generates significant internal friction, which produces the heat necessary to power its hundreds of active volcanoes.21

This process is so vigorous that it results in the constant resurfacing of the moon's landscape with lava and sulfur compounds, effectively replacing the entire surface every few thousand years.12