Does sonar detect iceburgs

Yes and no - all modern military submarines have special forward-looking and top-sounding under-ice Sonar systems that not only detect ice, but can give the approximate thickness of the ice as well.

The forward-looking under-ice system scans at a much higher frequency and is separate from the main sonar array. The top-sounding system is essentially a reverse fathometer, giving the distance from the boat to the ice surface as well as the ice thickness. Ice thickness is essential to know in situations where surfacing through the ice is required.

As for open water icebergs, the noise created by the water movement against the iceberg can be detected by passive sonar, and of course detected by active sonar, though active is rarely, if ever, used.

It should be noted that large icebergs that are big enough to be a navigation hazard are monitored and tracked by major nations, and that information is made available to all military and commercial vessels. Large-mass icebergs in the open ocean are more of a hazard to submarines than surface vessels since their depth and mass below the water is generally a lot more than what is seen above the waterline.