  Landslides exhibit intermittent gravity-driven downslope movements developing
over days to years before a possible major collapse, commonly boosted by
external events like precipitations and earthquakes. The reasons behind these
episodic movements and how they relate to the final instability remain poorly
understood. Here, we develop a novel 'endo-exo' theory to quantitatively
diagnose landslide dynamics, capturing the interplay between exogenous
stressors such as rainfall and endogenous damage/healing processes. We predict
four distinct types of episodic landslide dynamics
(endogenous/exogenous-subcritical/critical), characterized by power law
relaxations with different exponents, all related to a single parameter
$\vartheta$. These predictions are tested on the dataset of the Preonzo
landslide, which exhibited multi-year episodic movements prior to a
catastrophic collapse. All its episodic activities can be accounted for within
this classification with $\vartheta \approx 0.45\pm0.1$, providing strong
support for our parsimonious theory. We find that the final collapse of this
landslide is clearly preceded over 1-2 months by an increased frequency of
medium/large velocities, signaling the transition into a catastrophic regime
with amplifying positive feedbacks.
