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How and why small volcanic ocean islands collapse and move vertically up and down
Fernando O Marques1, Luísa P Ribeiro2, Christian Hübscher3
1EMEPC - Task Group for the Extension of the Continental Shelf, Paço de Arcos, Portugal. fomarques@gmail.com.
Scientific Reports
|January 30, 2025
Summary
Small volcanic islands can collapse, leading to complex vertical movements like uplift and subsidence. This occurs when both the volcanic edifice and its weak, sediment-rich substrate are unstable, as seen on Santa Maria Island.
Area of Science:
- Geology
- Volcanology
- Geophysics
Background:
- Volcanic island mass influences large-scale collapse and vertical movements, with large islands like Hawaii experiencing subsidence and landsliding.
- The vertical movement dynamics of smaller volcanic islands, potentially more complex than simple subsidence, remain less understood.
- Santa Maria Island (Azores) provides a case study for examining these processes in a smaller volcanic edifice.
Purpose of the Study:
- To investigate the role of mass in volcanic island stability and vertical movement dynamics.
- To analyze the collapse history and vertical movement of Santa Maria Island using geophysical data.
- To evaluate the mechanisms and triggers of sector collapses in small volcanic islands.
Main Methods:
- Acquisition and analysis of new onshore and marine geophysical data from Santa Maria Island.
- Interpretation of the vertical distribution of submarine and subaerial lavas to infer geological history.
- Numerical modeling to evaluate potential collapse mechanisms and instability factors.
Main Results:
- Santa Maria Island has experienced multiple sector collapses, evidenced by geophysical data.
- A complex vertical movement history (seamount-island-seamount-island) was inferred, indicating alternating subsidence and uplift.
- The island's evolution is linked to volcanic construction (loading-induced subsidence) and sector collapse (unloading-induced uplift).
- A weak substrate, likely marine sediments, is identified as a critical factor for instability.
- Proximity to the East Azores Fault may have triggered flank collapses.
Conclusions:
- Small volcanic islands can be susceptible to sector collapses, significantly impacting their vertical movement.
- Instability arises when both the volcanic edifice and its underlying substrate are weak.
- The findings suggest that similar processes may affect other volcanic ocean islands situated on marine sediments.
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