Researches on the cold water infiltration theory for the response mechanism of sudden drop-slow rise type of water temperature: a case study of Fe3+, Mn2+ variation in Beiwenquan hot spring of Chongqing associated with the Wenchuan Earthquake

Abstract：Water temperature observations in deep wells have been carried out in China for more than 20 years, but the researches on the mechanism of temperature response remain inadequate, and very few researchers have studied this mechanism for hot spring water. In this paper, the Beiwenquan hot spring of Chongqing was continuously monitored from May 1 to July 4, 2008. During the May 12 Ms 8.0 earthquake of 2008, the Beiwenquan hot spring about 400 km from the epicenter had a huge response to the earthquake. After the earthquake, three relatively high elevation springs were cut off, and the discharge of some other springs increased by nearly 50%. The concentration of Fe3+ and Mn2+ increased twofold on May 12 and then decreased gradually. On July 4, the concentration of Fe3+ and Mn2+ was the same as that on May 1. This is attributed to the active development of karst areas in the Jialingjiang River valley which has numerous fissures and cracks. Because of the earthquake, the higher elevation springs whose temperature was lower than that of other springs and surface water came from the fissures and infiltrated into the lower elevation springs. This process accelerated the vertical movement of the water and the mixing of different waters.