BOCONÓ FAULT &
LOS ZERPA MORAINE
Background Info
Interpretation ON
Texture
Facies
B&W
Stage 1
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18,000 - 13,000 years before present, the "Los Zerpa" river valley was occupied by a glacier that formed the moraine deposits that bound the valley today (1, 2). The glacier melt-water drained over the terminal moraine (1).
When the glacier began to retreat, fluvio-glacial sediments were deposited, forming an alluvial plain that is stil preserved nowadays in the upper part of the valley (3). The outward drainage continued to flow through the terminal moraine (1).
The strike-slip offset along the Boconó fault (4) opened a breach through the right lateral moraine (5) and the river started to drain through this opening. The old drainage through the terminal moraine was abandoned (1). The river started to incise the fluvio-glacial deposits of the previous stage and originated a terrace 20-25 m above the present-day river level (3). After some time the breach (5) was partially closed and new deposits filled the valley.
Present day. Repeated offsets along the Boconó fault have re-opened the breach through the right lateral moraine (5). The river has incised the previous deposits and has formed a second terrace 6-10 m above the present-day river level. Two terraces along the inner slope of the lateral moraine (2) witness this evolution.