Well considering that Krakatoa erupted in the ocean The ground shook in the wake of the blast which was heard over 4500km and was estimated to be equal to the detonation of over 21,000 atomic bombs. It is safe to say that if you detonated 21, 000 atomic bombs in the ocean it would have a similar effect.
and then... The Horizon Vanishes: Tsunamis
"...all of a sudden there came a great noise. We...saw a great black thing, a long way off, coming towards us. It was very high and very strong, and we soon saw that it was water" - From A. Scarth, 1999
Upon the third and catastrophic explosion of Krakatoa, enormous tsunamis were generated by the displaced water as the island collapsed into the caldera. These waves moved with great speed across the Sundra Straits reaching a height of around 40m tall before slamming into the nearby coastlines. Smaller tsunamis had pounded the local villages in the previous days eruptions but nothing compared to this mammoth wave. Many small coastal islands were completely submerged and as the wave hit the mainland islands of Java and Sumatra it ravaged towns and villages while stripping away nearly all vegetation. In some cases, whole towns of several thousand people were washed away in a flash destroying and sign they had ever been there. Accounts exist of villagers scrambling up inland hills to escape the waves. Often only the small top of a hill would be spared by the enormous current leaving former neighbors in great struggle with one another, while trying to maintain a safe position from the waves.
Many ships in the Sunrda Straits at the time of the eruption met a similar fate as the villagers on the coasts. Many were caught unaware in the torrent and thrown across the sea. Once such ship, the Berouw(seen right), was carried over a mile inland and deposited on a position 10m above sea level. However, some ships were fortunate enough to be maneuvered head-first into the swells only receiving minor injury onboard.
According to Dutch authorities, 90 percent of the over 36,000 deaths were attributed to the devastating tsunamis. Bodies lined the coasts for weeks and thousands of livestock were found throughout the Sundra Straits
On August 27th, 1883 a series of blasts on the island of Krakatoa culminated in a colossal explosion that blew the island apart in one of the largest eruptions in recorded history. Below are a few brief facts about the blast and its effects.
1. The 23km square island of Krakatoa existed at a height of 450m above sea level. The blast leveled most of the island to 250m below sea level.
2. Pyroclastic flows traveled as far as 40km from the island consuming traversing ships in fire and ash.
3. The sound of the final explosion was heard over 4500km away and covered 1/13th of the Earth's surface.
4. The eruption generated tsunamis 40m high that devastated nearby coastlines.
5. The final death toll from pyroclastic flows, volcanic bombs, and tsunamis was calculated to be a devastating 36,417.
Considering the fact that the atomic bombs that have been detonated have not even been heard or noticed by people I would say that a volcano is more powerful than any human bomb!