The Zailiysky Alatau located in a zone of high seismic activity. May 28, 1887 an earthquake occurred with a magnitude of 7.3. The landslides with the total volume of about 300 million cubic meters reached the territory of Almaty city. In the Prokhodnaya River valley landslide (debris flow?) with a volume of about 54 million cubic meters formed. Verification of hypothesis about genesis of landslide (debris flow?) was taken into account geomorphological, geological and hydrogeological structure of valley; data on ancient and modern glaciations; mineralogical and grain-size compositions of detritus; degree of rounding of boulders; weather (precipitation and air temperature) on the day of earthquake. As a result earthquakes landslides and debris flows caused by dissolution of loess massif are of great danger. In this connection defense against landslides, which can transform into debris flows, plays an important role in the sustainable development of the Republic of Kazakhstan.