The pilot of a skid equipped helicopter reported that after landing on a volcanic rock hill top, the pilot exited the running helicopter. The pilot further reported that he heard an audible change in the sound of the main rotor and observed the ground under the right skid of the helicopter give way and the helicopter rolled to the right. The helicopter sustained substantial damage to the tail boom. According to the pilot there were no preimpact mechanical failures or malfunctions with the airframe or engine that would have precluded normal operation. The Federal Aviation Administration (FAA) has published FAA-H-8083-21A Helicopter Flying Handbook (2012). This handbook discusses pilots at the flight controls and states in part: "Many helicopter operators have been lured into a "quick turnaround" ground operation to avoid delays at airport terminals and to minimize stop/start cycles of the engine. As part of this quick turn-around, the pilot might leave the cockpit with the engine and rotors turning. Such an operation can be extremely hazardous if a gust of wind disturbs the rotor disk, or the collective flight control moves causing lift to be generated by the rotor system. Either occurrence may cause the helicopter to roll or pitch, resulting in a rotor blade striking the tail boom or the ground. Good operating procedures dictate that, generally, pilots remain at the flight controls whenever the engine is running and the rotors are turning".