PROPOSED MECHANISMS:
The development of debris flows in the area appear to involve several stages including:
· movement of water to the failure sites (e.g. along fractures),
· initial failure by sliding (such as in slopes underlain by bedded strata),
· mobilization of the sliding mass as a flowing slurry; loose sediment available in the channels was also mobilized, and
· flow of the slurry as debris flows.
The resulting debris flows were facilitated by channels in the area.
Most of the damage in the Fellowship area, including the loss of lives, was due to the debris flows.
CONCLUSIONS:
This study provides basic guidelines that may be applicable to landslide loss reduction in the Fellowship area.
These are summarized below. Previous landslide events in the area support these suggestions.
1. Timing with respect to rainfall:
It appears that approximately 150 mm(~ 6 inches) of rainfall in 24 hours may initiate shallow landslides which may be quickly transformed into debris flows which are capable extensive damage.
2. Susceptible lithology and structure:
Hydrothermally altered, weathered and fractured andesitic rocks, and shale/mudstone bedrock are prone to slope failures.
3. Susceptible hillslopes:
failures have occurred on slopes modified for human use as well as in forest and brushland.
4. Most of the damage has occurred along debris flow chutes.
5. Since most of the damage following significant rainfall events in Jamaica is due to landslides, it is considered important that post-disaster surveys must include a proper documentation of landslide related damage.