7.9 Earthquake off of Tonga, no tsunami

As seen in this article, a 7.9 magnitude earthquake off the coast of Tonga did not produce a dangerous tsunami on the shores of Tonga, Samoa or Fiji and the tsunami alert for these island chains was cancelled. 

 Although small earthquakes are frequent, it's also good to note that the geographic features of Tonga not only the volcanic Islands above the water but volcanoes below the surface of the ocean apart of the Tonga-Kermadec arc which is an Intra-oceanic arcs that have oceanic crust on either side.  The islands are considered to be in the priximity of the Pacific ring of fire an area know to have frequent volcanic activity.  Other sub ocean suface Tongan geograhpy includes the Tonga Trench one of the word's deepest cen Trenches at approx. 10800m or 35,424ft  which means at it's deepest point, the Tonga Trench is deeper below the sea level than Mt. Everest is above sea level at approx. 29,028 ft.

This is a video of the gases from the undersea volcano near the Isles of Tonga rising above the surface of the ocean,