Photo by Haynes from the Gregory Jones Collection. Geysers are fragile, temporary, geologic features. Nature itself can destroy geysers.
Some geysers die because their water or heat source change, move or disappear.
This all is part of the natural processes that governs geothermal features. Man, however, sometimes hastens the demise of geysers. Debris thrown into their vents can block the throat of a geyser and block the eruptions. Over the years thoughtless visitors have damaged the world's geysers by throwing debris or foreign substances into thermal features. Some geyser areas are not well protected and vandalism, though sometimes present, is not the main threat to the hydrothermal features.