Moguls, sometimes known simply as bumps are formed by the skiers as they execute turns. Once a mogul has formed it tends to grow in size, because the moguls tend to encourgage skiers to follow similar paths. This can lead to a very large moguls which can be very daunting. Since skiing tends to be a series of linked turns moguls form together. In most ski resorts certain runs are left un-pisted (un-groomed) to allow moguls to develop.