What is the fine-grained topic of the following text: Starting on Tuesday morning in February 21, 1950 between 8.00 and 8.30 am with a roar, landslip caused quite severe local earthquake by slipping from the left side of the Sera valley and the rubbish formed a set about 650m in length and 350m in width, with 65 m in height. Only return the topic.
1950 Sera Valley Landslide and Earthquake