Characteristics Of Tension Fissures And Their Genetic Analyses On The Western Lava Flows Of Laoheishan Volcano, Wudalianchi

The geological systems of tension fissures are widely found in the regions of lava flows, ground subsidence and development of extension structures. However, the fissure systems on the basaltic lava flows are very outstanding, which are the important storage media and migration pathway of groundwater (or mineral water), oil and gas. Through the field observations of the tension fissures on the western lava flows of Laoheishan volcano and the uses of high-resolution remote sensing data, we explored and analyzed the information of the systems of tension fissures and attempt to reveal the law of their spatial distribution and their causes.The tension fissures on the western lava flows of Laoheishan volcano are very rich and have different length and width. According to the ability of high-resolution panchromatic band of Quickbird remote sensing data to identify the tension fissures with the width > 0.5 meter and the length of >3 meter, we took out the data of tension fissures on the western lava flows of Laoheishan volcano. Then the data were analyzed on their spatial distributions by the software of geographic information system. The spatial distribution characteristics of the tension fissures were also analyze and described, such as the distribution of fissure direction, the fissure length within unit area and the fissure number within unit area. After the determination of the overall advantage direction, we chose fifteen interest areas with amounts of tension fissures and studied the distribution characteristics of fissures in each interest areas, including advantage direction, the length and number of fissures within unit area.Some of these areas are the lava flows forming in the same period, while others are not. Their direction distributions reflect the characteristics of fissures in the area. In addition, we measured the information of area, perimeter and aspect ratio of twenty-one tumuli and lava collapse of larger sub-overflow in the edge of western lava flows of Laoheishan volcano, Wudalianchi. The conclusions are as follows:1. There exists the characteristic combination structures of the tension fissures in the western lava flows of Laoheishan volcano. These combination structures have close relationship with the different types and stages of lava flows.2. According to the interpretation of remote sensing data and the field observations, three groups of the fissure advantage-directions in the western lava flows of Laoheishan volcano are recognized, which reflects the directions of lava flows. The overall flow directions of large lava flows is east-west and north-west,but the north-east flow direction of lava flows may be the sub-overflow of large lava flows or the smaller ones.3. With the different distances between fissures and Laoheishan volcanic cone and the types of lava flows (sheet lava flows or small sub-overflows), the tension fissures show the different features.