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Methodology-Mapping 9 Miles Bull Bay -Bloxburg, St. Andrew, Jamaica
My mapping of the area took place on July 5, 2026. It started via vehicle on Gysum Drive for approximately 2km, and culminated via foot traversing predominantly the main & minor roads leading up to the Bloxburg community. My mapping by foot was a total of 17.64km; and the duration was 5hrs 50 minutes.
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My Thoughts on the Terrain
From Gysum drive looking up at the Hilly Terrain with steep & partially jagged cliff faces, I could tell that this section of the Wagwater fault zone, takes the brunt of compression Tectonism via the Wagwater fault system predominantly.
Lithology
The dominant lithology are as follows:
Grey, Recrystallized Impure Carbonate/Limestone
This lithology has a close association (intercalated at times), with the volcanics present. They generally appear as large boulders (.5m-over 20m in diameter) overhanging cliff faces. This lithology is karstic in texture.
Purple-Brown Volcanics
This lithology appears as volcanic clasts (purple, grey), that can be conglomerate or brecciated; as well as dominantly singular volcanic with basaltic makeup. The size of the lithology can range from pebble-sized to boulders over 2m in height. Zones of mafic, rustic-brown; green & blue-green in colour can be found with this lithology. Carbonate veins as well as Anhydrite/Gypsum zones can also be found in this lithology.
Grey-Brown Volcanics
This lithology is generally porphyritic in texture (mineral size range from1mm-3mm). They generally are present after encountering the purple-brown volcanics & impure carbonate. I interpret this lithology as a product of carbonate & basaltic magma mixing (Adakite condition that is also conducive for iron & copper Skarns formation).
Anhydrite/Gypsum
This mineral appear as grey-black banded makeup, with a somewhat foliated texture. The anhydrite/gypsum appear as 3 inches to half a meter thick beds in some sections throughout the area. They can be found in association with the purple-brown/grey-brown volcanic zones.
Geologic Cross-section: 9 Miles Bull Bay -Bloxburg, St. Andrew, Jamaica
Other Observations
Anhydrite/Gypsum Mine
This mine is still operational. According to residents of Bloxburg (over 60 years in age), the mine has been in operation for over 70 years. The residents went on to state that the mine is owned by Carib Cement (primarily in cement production). Near to where the mine entrance is, there are a few empty houses (apparently abandoned). As per the Bloxburg residents, the occupants of the houses were pushed to leave as a result of the operation of the mine.
Damaged Church (Bloxburg United Church), Due to Hurricane Melissa
A church with no roof was observed. As per the residents, the church was destroyed during the passing of Hurricane Melissa. The community of Bloxburg, with it’s landscape make up, support the pushing of wind upward. There is little to no wind-breaksupport available to the Bloxburg community. Based on my experience of feeling the wind whilst mapping, I could gather first hand just how the terrain supports the damaging effects of hurrican-force winds on the church.
Boulders partially blocking road(s); and overhanging sections of roads leading into Bloxburg
I observed boulders overhanging sections of the road leading into Bloxburg for approximately 3-5km. The size of the boulders range from .5metre-over 20metre in diameter. There is a section where a boulder with a diameter almost 2 metres in size partially blocks the road, with another being resisted by a tree stem. According to the residents, the boulder completely blocked the road during/after the passing of Hurricane Melissa. It took their efforts as a community, to clear the road enough for small vehicles to pass.
Similar to the above, I observed 2 boulders with a diameter of over 10metres overhanging the slope face near the Bloxburg community entrance. These boulders were being secured predominantly by the root network of trees.
The biggest boulder of them all, appears a section of a cliff/ridge. It sits precariously over the main road, entering the Bloxburg community. Similar to these observed boulders, large boulders of the Purple-Brown Volcanics also overhang some road sections leading into and out of (minor road), the Bloxburg community.
The Observation of Carbonates Boulder sized at 600+m & 800+m is testament of the Compression Faulting of the Wagwater Earthquake Zone
Throughout my traversing and mapping, I encountered carbonates and volcanics boulder-sized. Their dipping angle ranged from 50-86 degrees.
This observation is interpreted as highlights of the lithology and terrain, being uplifted as a result of Tectonism predominantly dominated by the active Wagwater Earthquake system.
Dominant Earthquake-Related Hazards Posed to Bloxburg and other nearby communities
- Boulder-sized Rockfall (houses, road users).
- Blocked Roads/marooning due to boulders greater than 1m in diameter.
