Ash blankets New Zealand.<br/> <br />Mount Tongariro made a surprise eruption after laying dormant for more than a century.<br/> <br />Experts said a pressure build-up of volcanic gasses caused the volcano to spew rocks and steam Monday.<br/> <br />(SOUNDBITE) (English) VOLCANOLOGIST, BRAD SCOTT SAYING:<br/> <br />"The eruption itself gave us no warning whatsoever, it just snuck up on us, and if further hydrothermal-driven eruptions occur they could well be the same."<br/> <br />Unlike a lava eruption, this volcanic activity was driven by steam.<br/> <br />Although the eruption had subsided by Tuesday, area flights were cancelled or delayed as clouds of ash lingered over the North Island.
