There is no evidence that magma beneath the enormous Yellowstone caldera is directly involved in the recent changes at Norris or Nymph Lake. Though magma as shallow as 3-6 miles beneath Norris does provide the heat for the geothermal system, the current activity is very unlikely to reflect magma ascent or increased likelihood of volcanism at Yellowstone Park. If magma were to rise to shallow levels beneath the ground it would be accompanied by intense swarms of local earthquakes and extensive displacement (deformation) of the ground surface around Norris. Thus far, caldera-wide seismicity and ground deformation have remained at typical background levels beneath Yellowstone and Norris.
O.K., I'll buy that.
But why has the park service closed Norris?
And what about my trout?