active danger geothermal geothermally hot landscape natural new zealand rock Rotorua seep sinkhole sulfur sulphur vapor vapour vent yellow boulder cloud colorado debris mountain nature precarious rocky rugged scree sky summit top unstable usa alert awareness birds black blue sky bright protection road crossing sign warning water birds water fowl wildlife big brooding cumulus England english Great Britain huge omen ominous Sussex threatening view America brew develop mountains panorama range storm bubble liquid Mineral Mud pool spout steam toxic bridge burst disaster engulf flood pond river road spate spating water winter accident fall hexagon hill hillside lichen mesh metal net netting pattern prevent rockfall safety secure texture wire bathing channel ground Maori village assistance beware drive help security street tow away traffic trail travel truck vehicle agricultural agrimotor machine traction-engine tractor