There is no doubt that disasters come from the hand of God:
Amos 3:6 ...shall there be evil in a city, and the LORD hath not done [it]?
Isaiah 45:7 I form the light, and create darkness: I make peace, and create evil: I the LORD do all these [things].
The current weather disasters everywhere may very well be building up to the end times, as we are seeing the natural disasters and wars and rumors of wars Jesus said would precede His coming.
2Pe 3:3-6 Knowing this first, that there shall come in the last days scoffers, walking after their own lusts, And saying, Where is the promise of his coming? for since the fathers fell asleep, all things continue as [they were] from the beginning of the creation. For this they willingly are ignorant of, that by the word of God the heavens were of old, and the earth standing out of the water and in the water: Whereby the world that then was, being overflowed with water, perished:
As to WHY the tsunami, we can only speculate, we can't know exactly. There is no such thing as a nation that doesn't deserve judgment. It's all a matter of timing. Scripture seems to teach that judgment comes at a point of accumulated transgressions, often after quite a long period of time, hundreds of years sometimes. When God commanded the Israelites to conquer Canaan, He told them that the transgressions of the Canaanites hadn't yet come to the point of punishment, the "fullness of time." Likewise all the other examples of national transgression and punishment foretold by the prophets, hundreds of years between the prophecy and the fulfillment in some cases. Not always. And there are many prophecies of judgment against the surrounding idolatrous nations as well, all of which are given to teach us how God deals with nations.
So, Indonesia is now mostly Muslim but formerly it was made up of many idolatrous tribes. God knows the causes, we can't. But there is no doubt that He is in charge of every specific circumstance of earthquakes and tsunamis. Nothing escapes Him.