These gaps are common & usually get filled quickly. "Getting filled" means the price action at a later time usually retraces at the least to the last day before the gap. The trading volume on such days is generally low / below average.
They occur when price action is breaking out of their trading range or congestion area. A good confirmation os such gaps is if they are associated with classic chart patterns (eg. Cup & Handle, Darvas Box, Ascending Triangle etc).
Volume will pick up significantly, for not only the increased enthusiasm, but many are holding positions on the wrong side of the breakout and need to cover or sell them.
Runaway gaps are also called measuring gapscaused by increased interest in the stock. Measuring gap will occur in the middle of, or half way through, the move. Note the significant increase in volume during and after the runaway gap.
Exhaustion gaps are those that happen near the end of a good up or downtrend. They are many times the first signal of the end of that move. Exhaustion gaps are quickly filled as prices reverse their trend.