LESSONS LEARNED

Our studies have helped in identifying the controlling factors and mechanisms that favour the occurrence of landslides on the island. These are summarized below and may be successfully used to mitigate the hazard:
A) Triggering mechanisms- Landslides are triggered both by earthquakes and heavy rainfall.
All earthquakes with magnitudes 4.5 and over have caused landslides and 200-300mm rainfall in 48 hours initiates shallow landslides that are quickly transformed into debris flows that cause extensive damage.
B) Landslides are strongly controlled by rock type and geologic structure with density of faults and joints being a very important factor.
C) It has been demonstrated that most of the slopes are pre-disposed to landslides, which control the evolution of slopes on the island. This model should guide the watershed management strategies. The significance and impact of landslides has not been previously recognized.
D) Damage from landslides is in most cases incorrectly ascribed to damage from floods. This must change if loss-reduction is to be achieved. In Jamaica, landslides frequently block the road network. This problem needs to be addressed promptly.
Our results may help road engineers. In addition to controls by bedrock and structure, we have found that the landslide densities within 90m of roads are several orders of magnitude more than that beyond 90m from roads.
Our results are supported by studies in Puerto Rico, which we have incorporated in our landslide modeling.