What would happen if the moon were twice as close to Earth?

Well, it was at one time. It was formed pretty close, then tidal friction has been moving it away. The closer distance may have been what made the Decca traps and other phenomena possible. Yes, higher tides, bigger earthquakes and all that.
  • Like
Reactions: rod
Pogo post #2 is accurate. In the giant impact model for the origin of our Moon, Theia hits and creates a proto-moon some 3-5 earth radii distance that expands outward away from Earth thru geologic time. Today the Moon's mean distance ~ 60.3 earth radii so the Moon about half this distance is some 30 earth radii. Extrapolating back to 3.5 billion years ago using present rate of recession for the Moon places the Moon's mean distance near 39 earth radii. For much of Precambrian geologic time, the Moon orbits closer to Earth (< 42 earth radii distance) with a much shorter lunar month and very large angular size in the sky compared to the present observations. Verifying these astronomical changes in the Moon's past orbit is challenging :) The solar eclipse and lunar eclipse cycle would be very different too than the present age, documented back some 3,000 years or so using Assyrian and Babylonian clay tablets recording eclipses.