Huge volume spikes are always worth looking in to, but there is more than one reason as why a huge volume spike would occur. But I agree, it's definitely worth looking in to. After a continued sell off, for example, a huge volume spike will often signal a bottom. One big down day with huge volume, usually means you can expect more move down. A big move up with huge volume, usually means you can expect some more upside. Why the volume, again, you'd have to look into each case separately.