Hi Bob

The geysers on Triton are believed to be entirely sublimation-driven phenomena caused by solid-phase greenhouse effect - heat trapped under nitrogen ice causes it to turn to gas, collecting enough for an eruption.

Nitrogen's triple point is at 63 K and neither Triton or Pluto is ever that warm on their surfaces normally. The triple point pressure for N2 is 0.125 bar, while the highest pressure on either world is measured in microbars. A recent study suggests there might be low level haze on Pluto obscuring its surface and so the pressure might be ~ 310 microbar and temperature about 43 K. Triton is ~ 38 K. Thus both are too chilly for either methane (freezes at 90 K) or nitrogen to exist in liquid phase except very briefly as a cryovolcanic eruption. Imagine a flow of a simultaneously boiling/freezing liquid and that's what you'd see. Perhaps a tunnel of ice might form over the flow allowing it to travel further.

Interestingly methane's critical point is at 190 K, some 13 degrees higher than the 176 K H2O/NH3 eutectic. Would be a weird world with both liquids existing, immiscible and one floating on the other, like oil on water. A bit like Nick's old "White Earth" idea with water overlying liquid CO2.