We present microwave (17 GHz) observations of eruptive activity in four solar coronal events with the Nobeyama Radioheliograph. These are weak events occurring at or near the solar limb associated with several types of activity: polar crown activity, prominence eruptions, and arcade flares. Morphological evolution of microwave sources in these events shows the following characteristic features in common: The activity starts as a mound-shaped source (1.0-4.5 X 10^4 km in height), above which a compact blob (< 1.0 X 10^4 km in size) appears later and expands horizontally toward the top of another low-lying mound. Finally a faint arch with a filamentary structure is formed, bridging the two mounds (0.2-2.0 X 10^5 km in horizontal scale size). Thus, the activity seems to propagate through the arch corridor from the initially activated mound to the secondary. During this process, the activity level increases, as indicated by an increase of the brightness temperature of the mound and the blob as well as by the formation of the arch and the eruption of the blob.

These common features suggest that basically the same energy build-up and release process takes place in all of the four events, in spite of the large difference in the total released energy. Here we propose magnetic reconnection progressing in between the blob and the mound as the basic process, as indicated by high-temperature plasma there, seen in soft X-rays. Our findings support a theoretically predicted analogy between filament (or prominence) activity and flare onset.