AbstractThe four craters, New Quebec, Clearwater Lakes (two craters) and Manicouagan are compared. New Quebec shows evidence of slow uplift accompanied by hydrothermal activity, possibly culminating in a minor volcanic outburst. Clearwater East is interpreted as the result of regional uplift followed by local collapse. Clearwater West shows similar features accompanied by a central peak and considerable volcanism. The latter two features are believed to be related. Manicouagan has a well developed central peak and an extensive volcanic pile. The characteristic cycle; upwarp, collapse, volcanism is beautifully shown. None of these craters can be explained either by ‘classical’ impact theory, or by analogy with known volcanic areas. New ideas are nee