Final answer:
An earthquake triggered the landslide in Indonesia that killed 19 people. Landslides can be caused by different factors, including heavy rainfall, volcanic eruptions, or deforestation, but the primary cause is always gravity acting on weakened slopes.
Step-by-step explanation:
The event that triggered a landslide, resulting in the deaths of 19 people in Indonesia was an earthquake. This natural disaster is one known factor that can create stresses and weaken slopes, ultimately leading to landslides, as described in historical events. For instance, on April 25, 2015, a 7.8 magnitude earthquake hit Nepal, causing an avalanche on Mt. Everest that led to fatalities, and similar disasters have occurred worldwide affecting many lives and landscapes.
Landslides can be induced by a variety of triggers. Among these are heavy rainfall, which saturates the soil increasing its weight and reducing its stability; volcanic eruptions, which can produce loose ash deposits and debris flows; and human activities such as deforestation, which can remove the stabilizing influence of tree roots on hillsides. In every case, gravity acting on weakened or over-steepened slopes is the primary cause of a landslide.