(1) The entire history is dependent on a single crucial process. It is the internal resistance represented by the bold upward arrow in the first shape.
(2) This process continues upward until it bursts out and creates the protrusion shown in the second shape.
(3) This process then bifurcates, creating the upper lobe shown in the third shape above. Involved in this stage is the introduction of a squashing process given by the bold downward arrow at the top of the third shape.
(4) Finally, the downward squashing process continues till it causes the new indentation in the top of the fourth shape above.