Tuesday 7 July 2015

Magnitude 6.2 Earthquake to the northeast of Tonga.

The United States Geological Survey detected a Magnitude 6.2 Earthquake at a depth of 10 km, about 70 km to the northeast of the island of Tongatapu (the largest of the 177 islands that make up the Kingdom of Tonga) slightly before 1.25 am local time on Tuesday 7 July 2015 (slightly before 12.25 pm on Monday 6 July, GMT). While this was a large quake, it was unlikely to present any danger due to its distance from shore, though it was felt on the island.

The approximate location of the 7 July 2015 Tonga Earthquake. Google Maps.

The islands of Tonga lie along the boundary between the Pacific and Australian Tectonic Plates. The Pacific Plate is being subducted beneath the Australian Plate along the Tonga Trench, which forms the boundary between these two plates, with the volcanic islands that make up the archipelago being formed as the subducting plate is melted by the heat of the planet's interior, so that lighter minerals rise up through the overlying plate as liquid magma, which fuels the volcanoes that build the islands. This subduction is not a smooth process, with the two plates constantly sticking together until the pressure generated by their movement builds up sufficiently to break them apart, causing a sudden forward jerk we experience as an Earthquake.

Diagram showing subduction along the Tonga Trench, and how this feeds the volcanoes of the Tonga Volcanic Arc. York University.

Witness accounts of Earthquakes can help geologists to understand these events, and the structures that cause them. The international non-profit organization Earthquake Report is interested in hearing from people who may have felt this event; if you felt this quake then you can report it to Earthquake Report here.

See also...

Flights to and from New Zealand have been disrupted following an eruption on Hunga Ha’apai, a submarine volcano in Tonga, on Monday 12 December 2015, producing an ash column 4500 m high and discolouring the sea red with ash, according to theWellington Volcanic Ash Advisory Centre. The volcano is...


Pumice is a volcanic rock, produced by the rapid cooling of gas rich lava from submarine eruptions, or high-pressure eruptions on land. The rapid cooling traps bubbles of gas within the rock, creating a very light material that will often float on water. Submarine volcanic eruptions can produce vast mats of...



On Thursday 9 August 2012 the Royal New Zealand Air Force spotted a raft of pumice-stone (volcanic rock filled with gas bubbles that floats on water) covering an area nearly 26 000 km², roughly 1000 km north  of North Island, in the Kermadec Islands, a New Zealand possession. This discovery was later confirmed by the Royal New Zealand Navy ship HMNZS Canterbury...



Follow Sciency Thoughts on Facebook.