They are dependent events because the outcome of B completely depends on what happened on A. Another notation to represent the probability of a series of dependent events is P(A|B), it is read as The probability of A given B.
Two events A and B are said to be independent if the fact that one event has occurred does not affect the probability that the other event will occur. If whether or not one event occurs does affect the probability that the other event will occur, then the two events are said to be dependent.