Study on the Frozen Cracks in the Lower Reaches of Yellow River

Key words: 
• frozen crack /
• Yellow River

Abstract: The lower reaches of Yellow River isfrozen in winter, asa result, a lot of frozen cracks are developed. They are noticeable with unusual appearances. All the frozen cracks may be broadly divisible into eight types according to their shapes including fissure-like,pod -like, linear, triple-junction -like, sawtooth-like, netty, spiral and branched.The fissure-like crack hassimplest shape. It is a straight, narrow, short fissure in plane and is a slaty sheet in space. The length is mostly below ten centimeters, and the width is not beyond one centimeter, and the depth is also mostly below ten centimeters. The both ends of the crack is sharp and flat, and the widdle is relatively wide and in relief.The cross section is like “v”. The length is several centimeters to more than ten centimeters, and the width is one to two centimeters and the depth is one to three centimeters. The straight linear frozen crack has a relatively simple shape and but the sizes are variable. The smaller one is decades of centimeters in length and several centimeters in width and in depth. The length of larger ones is in the range of from decades of meters to more than one handred of meters, and the width and depthe are all below ten centimeters. Commonly, they extend along the river course. The triple-junction -frozen-cracks are rather similar to triple junction rifts, but their sizes are considereblely small. In fact, they are an assamblage frozen cracks,being consisted of three single frozen cracks with an interangle of about 120°.The compound ones mean that large net contains small net and the simple type has only one rank. This netty frozen crack that consists of a series of straight linear frozen cracks is relatively complex. The sawtooth-like frozen cracks is actually an assemblage type that is made up of a series of short, linear frozen cracks with an interangle of about 120°. Also,their sizes are small and their length range mostly from ten to thirty centimeters and their width are not beyond one centimeter. The netty frozen crack is a rather complicated type. That consists of straight linear and curved frozen cracks. It may be divided into two types: Compound type and simple type. It may be divided into two to three ranks. The single frozen crack is straight linear or slightly curved and its length is several centimeter to decades of centimeters and its width is several millimeter. Also, the spiral frozen crack is an assemblage type, but their patterns are considerably unusual and single frozen crack has spiral form and several frozen cracks assemble to form flower-like pattern. The single frozen crack is in the range of five to forty centimeters in length and several millimeters in width. The branched frozen crack is rather complex in form and, also, is an assemblage type. Genenally, the size is small and the length is mostly in the range of ten to twenty centimeters and the width is below one centimeter. The last two type genenally develop in thin mud layer and the other generally develop in silt layer. Another frozen crack( frozen parting)is also considerably noticeable. The formation of frozen cracks,undoubtedly,is related to ice action and the interaction of ice melting and ice wedging is their concrete dynamatic process.