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Looking down on an idealized volcano from above. R is the radius of the cone at sea level. Angle A is portion of the circumference that will slide. In many cases the look-down profile of a volcano is closer to an ellipse than a circle. For example the caldera at Toba on Sumatra to the northwest is roughly an ellipse with a major to minor axis ratio of 3:1 (a circle would be 1:1). A more general solution would be to allow point collapse to be somewhere in the interior so not necessarily at the center. Likewise, the slope collapse need not start at the peak and extend to the circumference. A key difference is whether the slope collapse exposes the magma to seawater.