Short answers, pulled from the story.
Landslides occur when the shear stress on a slope exceeds the shear strength of the slope material. Common triggers include heavy rainfall that raises pore water pressure, earthquakes that destabilize slopes or induce soil liquefaction, and human activities such as deforestation, mining, and road construction that remove slope support or add weight.
A debris flow is a rapid, fluid-like movement of mixed material including water, broken timber, and rock, capable of blocking rivers and bridges. An earthflow is slower, involving mostly fine-grained material like clay and silt, and can move at speeds as low as 1 mm per year, though it can accelerate during periods of high precipitation.
The Vargas mudslides in Venezuela in December 1999 caused tens of thousands of deaths following extreme rainfall in Vargas State. The Monte Toc landslide on the 9th of October 1963 in Italy killed around 2,000 people when 260 million cubic meters of rock fell into the Vajont Dam basin and generated a megatsunami.
A rock avalanche, also called a sturzstrom, is a large, fast-moving landslide that travels far beyond what slope angle alone would explain. The long runout is thought to result from frictional heating in the shear zone, which can vaporize trapped water and build pressure, or grind rock into nanometer-scale powder that acts as a lubricant.
Yes. Submarine landslides and rockfalls into water can generate tsunamis, including megatsunamis hundreds of meters high. The Storegga Slide off Norway around 8,000 years ago displaced 3,500 cubic kilometers of material and caused massive tsunamis around the North Sea. A megatsunami also struck Lituya Bay in Alaska in 1958.
Climate change has mixed effects depending on region. Increased evapotranspiration and vegetation growth can stabilize some slopes. However, accelerated snowmelt, permafrost degradation at high elevations, glacier retreat, and more frequent heavy precipitation events all increase landslide risk in many areas. Weather extremes are expected to intensify, raising the frequency of debris flows triggered by concentrated rainfall.