Because liquid water is unstable at present venusian surface conditions, the discovery of channels (termed ''canali'') on Venus thousands of kilometers long was not predicted. Low-viscosity lavas that remain fluid for several thousand kilometers are considered to be the canali-forming agents; possible compositions of venusian canali-forming lavas include komatiite and high-Fe-Ti ''lunar''-type basalts. Results of analytical and numerical models of these lavas reveal that total cooling is more efficient on Venus than on Earth, suggesting that venusian lavas rapidly form insulating crusts, and, thus, that the canali lavas were essentially ''tube-fed.'' The models also reveal that thermal erosion should be less efficient on Venus than on Earth, suggesting that venusian channels are either the product of mechanical (rather than thermal) erosion or constructional processes. ¿ American Geophysical Union 1993