For what you deem it worth 2:
It is tough to compare anything to Tunguska as there is still far too much that is unknown about that object.
Given an object 30-50 meters in diameter…
This does not provide near enough information to do any calculations as there are a good number of quantities that must be known, or estimated: density, angle of entry, velocity at entry into the atmosphere, etc, etc, etc.
Further there are any number of models for the loss of energy (ground blast, air blast) to name only one, so one has to choose the best model relative to circumstances and the quantities you want to find.
Saying all that, I actually broke down and did some calculations to show low and high-end possibilities.
LOW but not LOWEST
I assumed a porous object (to obtain density). I assumed a low entry velocity, and 45 degree entry angle. The target material as you will see that is moot. The other assumptions are more technical so I’ll omit them.
Its maximum energy at entry would be about 3.4 megatons, 1.4x 10^16 joules.
This type of object would break up around 50 miles up. By about 8 miles from the ground it is completely broken up. Relatively large pieces may hit the ground but the entire object was only 50 meters to start.
The energy of the airburst would be about 3 megatons. No atmospheric effects (pressure change) would be felt at even 10 miles from the explosion. You can see about a ten percent loss of energy from the maximum at this point already.
The damage done on land would be that of about a 3 megaton weapon. The height could significantly mitigate this relative to a weapon detonation because of the extreme height at detonation of this object. Conclusion: you don’t want to be there.
I assumed an iron object (to obtain density). I assumed a maximum entry velocity, and 45 degree entry angle, and the target material as 1000m deep ocean. Again, the other assumptions are more technical so I’ll omit them.
Its maximum energy at entry would be about 35 megatons, 1.5x 10^17 joules.
This type of object would be broken but survive to form an impact crater on the seabed soccer stadium in size. At 15 miles the event would be less than 3 on the Richter scale. In 5000 meter ocean there is no crater >> 1 ft crater.
A friend continued some calculations in more detail for me and found that only about 100 cubic meters of material would be vaporized. Not my field but these seem to be rather small for generating tsunamis. I think amount of material subsidence is more important that amount total energy, again geology is not my field.
I am not sure what this is supposed to mean:
Second a water hit would be far worst then a ground inpact, except for the people directly under it, as the energy that would escape back into space as heat in a ground inpact would instead be turn into tide waves and stream/vaper by the 100 of meg ton.
There is no multiplication effect, starting with an energy of 3.4 megatons or 34 it cannot produce “100 of meg ton” effect just because it hits water.
The energy even in water only 1000m deep doesn’t seem to me sufficient to possibly cause tsunamis. Although I know that was reported in the press. The numbers say otherwise. There can be some significant local effects.
Rather than get into a long review of the physics of this I’ll just point out some history. During the bomb tests in the Pacific after WWII they detonated devices of this order; a 13.2 megaton device (for example) at Enewetak Atoll (on a barge sitting in the ocean). No regional, let alone global oceanic effects at all. A few low-lying nearby islands were affected.