Why was an iceberg powerful enough to sink The Titanic?

Arctic Ice is extremely hard and the cold makes the metal brittle. The combination is not good. Some people say the Titanic metal was especially susceptible but it has occurred more than once. It recently happened to a modern ship, the MS Explorer in 2007.

Because 90% of an iceberg is underwater. The part that was above water might not have looked like much, but when you consider what you can't see, its at least 100 times bigger than the Titanic. And it's made of solid ice. Something has to give in that collision, and it wasn't going to be the iceberg.

The iceberg was not powerful. It had no power of its own.

There are actually several factors that contributed to Titanic's sinking, not the least of which were icebergs. They can actually be just as dangerous to present-day boats as they were back then.

Factor 1: Early April is a hazardous time to sail any ships through the North Atlantic, particularly along the route Titanic was taking. There are still icebergs about from wintertime, and not all have melted just yet. The ship was sailing further north in that region of the ocean than all other steamships at the time, which was a dangerous move to start with. Titanic actually received several Ice Warnings by telegraph, and promptly ignored them. It wasn't until they were right on top of one on that fateful night that it became a problem.

Factor 2: The White Star Line was showing off with their new ship. They wanted bragging rights to how fast she was. That included getting as fast to New York from Liverpool as possible. She was moving at at an average of 21 knots (24 mph), which was extremely fast for that era. It was also reckless. Her speed was part of the reason they couldn't bank fast enough to avoid the iceberg, as well as the primitive communication tech being used between the guys in the crow's nest and the engine rooms down below. Ever tried driving a car at 80 mph and doing a sudden hairpin turn to your left to avoid a boulder? I think you can guess how that would turn out.

Factor 3: As we saw with what Mr. Andrews showed everyone in the meeting room, the bulkheads were not very well-designed. He thought it was a great idea to only build them up to E-Deck, rather than have them go all the way up to under the Boat Deck. (This was probably to save money on the iron used to build the bulkheads). That design flaw was one of many reasons why the ship couldn't take the damage it got. He said they could handle 4 compartments getting damaged and flooded, but not five, like what had happened with the iceberg. Because the first 5 compartments of the ship had been flooded, the ship was now too heavy to achieve buoyancy, and the pumps would not be able to keep up with the seawater. The water would continue to fill and spill over the bulkheads into the compartments behind them, until the ship went down.

So it wasn't any one thing that took Titanic down, but the iceberg was the key factor in its sinking. The rest was just a cascade of events leading up to and contributing to the disaster. There are more factors, but they aren't relevant to the iceberg.

I don't think the design was all that faulty. It was never intended to be able to survive that kind of collision.

Icebergs do not have any power at all. They just sit there, moved by the currents of the ocean. It was the power of the Titanic's momentum that ran it into the iceberg, rupturing it's weaker than thought hull.