BTCUSD
Gonna describe a) and b) here. As you can see on a) we had the first real sell off, the future ones not being that heavy, at least volume wise, and even that last one on our way to 6000, volume wasn't so hot. On b) volume left traces, we had much more supply to get rid of. As you can clearly see, they are the biggest bars on the chart, indicating supply has been taken care of, and there is not much else to sell.
But wait, theres more
Price is still falling... volume is flat, and going down a bit, sell volume.
Doesn't it remind you of what happened in number 1? Finally a red bar after a good bull run, then decreasing buy volume, but SIKE! We pump! This might be happening right now, but in reverse.
Price is still falling, but there is no interest in it still falling, as it seems all supply has been sold off. So, volume is stale and SIKE! We dump! Finally looking to have found the bottom, we now start another cycle, looking to tinker with the high 20,000s for the first time ever.
Conclusion: bottom is very near.