Sciency Thoughts: Santa Cruz Islands

Showing posts with label Santa Cruz Islands. Show all posts

Saturday, 7 April 2018

Magnitude 5.3 Earthquake to the southwest of Santa Cruz Island, California.

The United States Geological Survey recorded a Magnitude 5.3 Earthquake at a depth of about 9.9 km, roughly 29 km off the southwest coast of Santa Cruz Island, California, slightly before 12.20 pm local time (slightly before 7.20 pm GMT) on Thursday 5 April 2018. There are no reports of any damage or injuries relating to this quake, but people have reported feeling it across much of southern California, and as far inland as Las Vega in Nevada.

The approximate location of the 5 April 2018 Santa Cruz Island Earthquake. USGS.

California is extremely prone to Earthquakes due to the presence of the San Andreas Fault, a tectonic plate margin that effectively bisects the state. The west of California, including Santa Barbara and Los Angeles, is located on the Pacific Plate, and is moving to the northwest. The east of California, including Fresno and Bakersfield is on the North American Plate, and is moving to the southeast. The plates do not move smoothly past one-another, but constantly stick together then break apart as the pressure builds up. This has led to a network of smaller faults that criss-cross the state, so that Earthquakes can effectively occur anywhere.

The extent of and movement on the San Andreas Fault. Geology.

Witness accounts of Earthquakes can help geologists to understand these events and the underlying structures that cause them. If you felt this quake (or if you were in the area but did not, which is also useful information) then you can report it to the United States Geological Survey here.

Saturday, 28 October 2017

Eruptions on Mount Tinakula.

The Wellington Volcanic Ash Advisory Center reported an eruption on Mount Tinakula, an uninhabited island stratovolcano (cone-shaped volcano made up of layers of ash and lava) at the north end of the Santa Cruz Islands (part of the Solomon Islands), on the morning of Saturday 21 October 2017, which produced an ash column that rose to a height of 4.6 km and drifted to the north. A second, larger, eruption about four hours later produced an ash column that rose to a height of 10.7 km. Eruptions on the island continued for the rest of the week, producing ash falls on the islands of Fenualoa, and Nupani, and tainting water supplies in parts of the Reef Islands.

Satellite image of an ash column over Mount Tinakula taken by the MODIS camera on the Terra Satellite on 28 October 2017. Position of volcano indicated by yellow triangle. NASA/Volcano Discovery.

The Santa Cruz Islands lie on the boundary between the Australian Plate (to the south) and Pacific Plate (to the north). The Australian Plate is moving northward relative to the Pacific Plate, and being subducted beneath it. As the plate sinks further it is partially melted by the heat of the friction combined with that of the Earth's interior. Some of the melted material then rises through the overlying Pacific Plate, fuelling the volcanoes of the Santa Cruz Islands.

Thursday, 23 February 2012

Possible eruption on Tinakula.

Tinakula is a volcanic island in the Santa Cruz Islands, part of the Solomons, roughly 500 km east of San Cristobel, or 500 km north of Vanuatu. The island forms the peak of a massive stratovolcano (cone shaped volcano) rising 3-4 km from the sea floor to form an island 3.5 km across and 851 m high. The summit crater of Tinakula was breached by a landslide in 1965, forming an open scarp on the west side of the island that runs down to the sea.

Due to its remote location Tinakula is not visited very often, and so is not monitored from the ground. However it is visible to satellites, allowing a level of surveillance. On 13-14 February 2012 NASAs MODIS Instrument detected increased heat coming from Tinakula, and on 14 February the Earth Observing-1 satellite imaged a plume of ash and smoke issuing from the summit of the volcano.

Image of Tinakula captured by the Earth Observing-1 satellite on 14 February. Scale bar is 500 m. Earth Observatory.

Eruptions of this kind do not seem to be unusual on Tinakula. Satellites detected similar activity in 2004, 2006, 2007, 2009, 2010 and 2011. Eruptions were observed by boat in 1984 and 1985, and an eruption in 1971 was observed by airplane and seen from Trevanion Island, 20 km to the south; this eruption caused a small tsunami, though no-one was hurt. Numerous other explosions have been recorded on the island since its discovery by the Spanish in 1595. The island was inhabited till about 1840, when the entire population was wiped out in a particularly violent episode. Since then there have been sporadic attempts to colonize Tinakula by people from neighboring islands, but all have been abandoned.

The Santa Cruz Islands are a volcanic island arc on the boundary between the Pacific and Australian Plates. The Australian Plate is being subducted beneath the Pacific Plate. As it sinks into the Earth's interior it is heated, and partially melts. Some of the melted material rises through the overlying Pacific Plate as magma, forming the volcanoes of the Santa Cruiz Islands, including Tinkula.