Formation of nonintersecting nested calderas: insights from analogue models

Approximately 56% of 60 known nested calderas are pairs of nonintersecting subcircular structures with similar eccentricities. The consistent configuration suggests an interdependence in the formation of the two annular structures. This possibility has been investigated using 11 analogue models with sand (crust analogue) overlying silicone (magma analogue). Silicone withdrawal induces collapse within the sand, forming two concentric depressions: the first-formed inner depression, bordered by outward-dipping reverse ring faults (mean dip of 75 degrees), induces the collapse of the outer depression, bordered by inward dipping, normal ring faults (mean dip of 84 degrees). An original linear relationship is determined among the ratios between the diameters of the two depressions and the depth of the ring faults. Selected pairs of natural nested calderas show similar proportions, highlighting a consistent architecture. This suggests that some pairs of nonintersecting nested calderas result from a single collapse event.