I understand that there is an on-line site, named Impact Earth!, that allows us to calculate the damage caused by an impact of an asteroid using some parameters.
In my novel, I have an impact from a solid rock with approximately 500 meters in diameter on the ocean bed, free falling at a 90º angle.
Trouble is, the calculator only allows for a minimum velocity at impact of 11 Km/sec since that is the lowest speed an asteroid may hit the Earth.
But my solid rock isn't an asteroid, but rather one of these airborne islands, floating 1.500-2.000 meters above ground. The initial velocity would be 0, so, according to my calculations, it would hit the surface of the sea at a velocity of 170-190 m/sec, much lower than the minimum velocity of 11 Km/sec allowed by Impact Eart!
Could anyone help me with these calculations?... I am interested mainly on the height of the tsunami waves and on any atmospheric changes that would be visible (if any).
Note: I have yet to decide on the ocean depth and the distance from the coast at the site of impact... I would like the impact to be relatively near the shore, maybe some 3 to 5 Km away from the beach.