The details of volcanic plume source conditions or internal structure cannot readily be revealed by simple visual images or other existing remote imaging techniques. For example, one predominant observable quantity, the spreading rate in steady or quasi-steady volcanic plumes, is independent of source buoyancy flux. However, observable morphological features of short-duration unsteady plumes appear to be strongly controlled by volcanic source conditions, as inferred from our recent work. Here we present a new technique for using simple morphological evolution to extract the temporal evolution of source conditions of short-lived unsteady eruptions. In particular, using examples from Stromboli (Italy) and Santiaguito (Guatemala) volcanoes, we illustrate simple morphologic indicators of (1) increasing injection rate during the early phase of an eruption; (2) onset of source injection decline; and (3) the timing of source injection cessation. Combined, these observations indicate changes in eruption discharge rate and injection duration, and may assist in estimating total mass erupted for a given event. In addition, we show how morphology may provide clues about the vertical mass distribution in these plumes, which may be important for predicting ash dispersal patterns.