Complex sentence: At the surface, the seiche in Lake Michigan may be barely a ripple while below the surface it is usually about 30 feet high and at times may grow to a height of 300 feet!! !
Split into simpler sentences: At the surface, the seiche in Lake Michigan may be barely a ripple or it may grow to more than 30 feet high. Below the surface, a seiche at times may grow to a height of 300 feet!!!