These plumes can reach heights of up to a few thousand km above the planet’s surface where they cool and spread out, in the process, obscuring the underlying thermal emission from the planet. Plume heights of a few thousand km appear otherworldly when compared with volcanic plumes on Earth. However, such plume heights are quite plausible since Jupiter’s moon Io can spew volcanic plumes with heights of up to roughly 300 km to 500 km, or 0.16 to 0.27 times the radius of Io itself.
The high temperature on 55 Cancri e results in a weak planetary crust, perhaps even a molten surface. This is probably the reason behind the intense volcanic activity that is thought to be occurring on 55 Cancri e. Small exoplanets (i.e. about the size of Mercury) that are highly irradiated can have material simply erupting directly into space. However, such a mass-loss is unlikely for 55 Cancri e as it is much more massive and has a much stronger gravity. Instead, material from the volcanic plumes on 55 Cancri e will fall back onto the planet’s surface.
Demory et al. (2015), “Variability in the super-Earth 55 Cnc e”, arXiv:1505.00269 [astro-ph.EP]