an undersea volcanic eruption
... that an undersea volcanic eruption which produced a pumice raft covering approximately 10,000 square miles (26,000 km2), was not discovered until several weeks had passed?
... that <b id="mwB64"><a class="mw-redirect" href="./2012_Kermadec_Islands_eruption_and_pumice_raft" id="mwB68" rel="mw:WikiLink" title="2012 Kermadec Islands eruption and pumice raft">an undersea volcanic eruption</a></b> <i id="mwB7A">(pictured)</i> which produced a <a href="./Pumice_raft" id="mwB7E" rel="mw:WikiLink" title="Pumice raft">pumice raft</a> covering approximately <span about="#mwt28" data-mw='{"parts":[{"template":{"target":{"wt":"convert","href":"./Template:Convert"},"params":{"1":{"wt":"10000"},"2":{"wt":"sqmi"}},"i":0}}]}' id="mwB7I" typeof="mw:Transclusion">10,000 square miles (26,000</span><span about="#mwt28" typeof="mw:Entity"> </span><span about="#mwt28">km</span><sup about="#mwt28">2</sup><span about="#mwt28">)</span>, was not discovered until several weeks had passed?