Kolumbo submarine volcano lies 7 km NE of Santorini caldera and its last eruption which occurred in 1650 AD, caused damage and casualties to the nearby islands. Here a simple model of a chamber, containing silicic magma underlain by a smaller quantity of mafic magma, is utilised in order to understand the chamber behaviour during the 1650 AD eruption. Results show that in order to reproduce the duration (83–281 days) and the dense rock equivalent volume (\({\sim }\,2\, \hbox {km}^3\)) of the eruption, initial overpressure in the chamber should be around 10 MPa and the mafic magma should occupy up to 5% of the chamber volume. It is found that the time needed to inject mafic magma equal to 1–15% of the chamber volume varies between 1.4–13.7 ka, if the radius of the chamber is about 1500 m as inferred from tomographic images. These long recurrence times agree well with the small number of eruptions (\(N = 5\)) within a period of > 70 ka and suggest that an eruption in the near future is unlikely. Volcanic activity at Kolumbo is probably triggered by a combination of exsolved volatiles and a small but steady influx of mafic melt in the chamber.