Fernandina's caldera is over 1100 feet deep. At times, a small lake has formed in the north part of the caldera.
Calderas form as a result of collapse following magma withdrawal from the underlying magma chamber.
The calderas of the Galapagos probably form from multiple collapses. The collapse followed a brief eruption at an elevation of about 700 m on the eastern flank on May 21. At 10 AM on June 11, an earthquake occurred and was followed by the rise of a large white cloud that was visible from Santa Cruz. At 5 PM a large boom was heard and was followed by smaller exposions for several hours and a number of earthquakes that lasted over a week, the largest of which was a magnitude 5 occurring on June 15. A party from Darwin Station reached the summit on June 19, but could see little because of the dust generated by constant avalanches.