I am working on a survival suspense story, where a sizeable group of surivors is trapped in a tropical island (somewhere in the Ring of Fire) by a volcanic eruption. They find shelter from the erpution in an old mansion built in a high-rise cliff on the edge of the island.
The cliff is sturdy and the mansion is stonemasonry, so there is little danger of fire from cinders or a collapse.
The eruption I am visualizing would have a Volcanic Explosivity Index of 4 to 5. Most of the inhabitants and tourists of the island died because of the pyroclastic flow and other eruption hazards. Only the few that climbed the hill leading to the cliff survived because the pyroclastic flow goes downhill, and there is a sizeable valley between the volcano and this hill.
They are cut off from rescue for a long period of time (so I can play with isolation, food shortage and so on), so I need the mansion to survive the eruption and remain in the extreme end of habitable (temperature, etc - almost inhospitable). Sickness from inhaling ashes and heat strokes are hazards that will claim some survivors, but a handfull must survive to the end.
The lava flow would reach the ocean before climbing the cliff, but isolated the group from the rest of the island, and is too close for confort, but they can still venture outside the manor for short periods of time.
How close can I put the mansion from the lava flow and/or the volcano caldera so not to push the suspension of disbelief?