Would a Hovercraft Set off a Landmine?

Just setting it would be highly dangerous, and virtually anything could set it off. 7 psi is half an atmosphere; not very much. Also, you should differentiate between antipersonnel and anti-tank mines. The former might not be well designed to damage a hovercraft (e.g. Google Bouncing Betty).

How much force does it take to set off a landmine?

These mines are pressure activated, but are typically designed so that the footstep of a person won't detonate them. Most anti-tank mines require an applied pressure of 348.33 pounds (158 kg) to 745.16 pounds (338 kg) in order to detonate. Most tanks and other military vehicles apply that kind of pressure.

What triggers a landmine?

A land mine can be triggered by a number of things including pressure, movement, sound, magnetism and vibration. Anti-personnel mines commonly use the pressure of a person's foot as a trigger, but tripwires are also frequently employed.