Chronology of Christmas Island's volcanic history unearthed

Researchers established the age of the various rocks on Christmas Island at the time they were erupted, and established the position of the island through time. 

Credit: Peter McKiernan

Geological samples from Christmas Island have been analysed by a West Australian scientist, giving valuable insight into its unique volcanic history.

Curtin University geochronologist Dr Fred Jourdan says while continents are often the subject of geological investigation, ocean geology is less studied and the results of the Christmas Island study adds important information to the field.

The report he co-authored has been published in Gondwana Research.

It describes the Christmas Island area as an extensive zone of volcanism in the north-east Indian Ocean, consisting of numerous submerged seamounts and flat topped guyots.

It explains the island has experienced multiple episodes of volcanism that are exposed sporadically along its coastline.

It is the only island in the region to show intraplate volcanism in the form of basaltic rocks that are exposed above sea level.

Dr Jourdan says the project was a collaboration with Macquarie University. Samples were collected by a student from Macquarie University and tested at Curtin University using 40Ar/39Ar geochronology and paleomagnetism.

Dr Jourdan says this is where the 'real science' of finding their origin began.

"What we did was two things; we established the age of the various rocks on the island at the time they were erupted, and we established the position of the island through time," he says.

"We needed to look at where it was before, to understand why there is volcanic activity at all—is it random or related to something in particular?

"We measured two different ages but we know, comparing it to other seamounts, there are in fact three periods of volcanic activity.

Three stages of Christmas Island volcanic activity

"The oldest happened when Australia and India separated and the rock left behind melted to create a seamount—that was the first volcanic activity, although we didn't sample this and at this time, the island was much further south than it is now.

"The second, happened between 43 and 37 million years ago—it happened when the continent moved north above a hot zone in the mantle.

"Nothing happened for 30 million years until, in its northward movement toward the European-Asian plate; the plate cracked five million years ago and the magma could easily rise through the cracks."

Dr Jourdan says similar low volume intraplate volcanism had previously been observed at similar tectonic settings to the Japan and Tonga trench.

"…We put forward the Indo Australian plate subduction setting as a likely candidate for this phase of introceanic volcanism."

More information: Rajat Taneja, Craig O'Neill, Mark Lackie, Tracy Rushmer, Phil Schmidt, Fred Jourdan, "40Ar/39Ar geochronology and the paleoposition of Christmas Island (Australia), Northeast Indian Ocean," Gondwana Research, Available online 27 April 2014, ISSN 1342-937X, dx.doi.org/10.1016/j.gr.2014.04.004.

PanSTARR-1: Ten thousandth near-Earth object unearthed in space

Asteroid 2013 MZ5 as seen by the University of Hawaii's PanSTARR-1 telescope. In this animated gif, the asteroid moves relative to a fixed background of stars. 

Asteroid 2013 MZ5 is in the right of the first image, towards the top, moving diagonally left/down. Credit: PS-1/UH

More than 10,000 asteroids and comets that can pass near Earth have now been discovered.

The 10,000th near-Earth object, asteroid 2013 MZ5, was first detected on the night of June 18, 2013, by the Pan-STARRS-1 telescope, located on the 10,000-foot (convert) summit of the Haleakala crater on Maui.

Managed by the University of Hawaii, the PanSTARRS survey receives NASA funding.

Ninety-eight percent of all near-Earth objects discovered were first detected by NASA-supported surveys.

"Finding 10,000 near-Earth objects is a significant milestone," said Lindley Johnson, program executive for NASA's Near-Earth Object Observations Program at NASA Headquarters, Washington.

"But there are at least 10 times that many more to be found before we can be assured we will have found any and all that could impact and do significant harm to the citizens of Earth."

During Johnson's decade-long tenure, 76 percent of the NEO discoveries have been made.

Near-Earth objects (NEOs) are asteroids and comets that can approach the Earth's orbital distance to within about 28 million miles (45 million kilometers).

They range in size from as small as a few feet to as large as 25 miles (41 kilometers) for the largest near-Earth asteroid, 1036 Ganymed.

Asteroid 2013 MZ5 is approximately 1,000 feet (300 meters) across. Its orbit is well understood and will not approach close enough to Earth to be considered potentially hazardous.

"The first near-Earth object was discovered in 1898," said Don Yeomans, long-time manager of NASA's Near-Earth Object Program Office at the Jet Propulsion Laboratory in Pasadena, Calif.

"Over the next hundred years, only about 500 had been found. But then, with the advent of NASA's NEO Observations program in 1998, we've been racking them up ever since. And with new, more capable systems coming on line, we are learning even more about where the NEOs are currently in our solar system, and where they will be in the future."

Of the 10,000 discoveries, roughly 10 percent are larger than six-tenths of a mile (one kilometer) in size - roughly the size that could produce global consequences should one impact the Earth.

However, the NASA NEOO program has found that none of these larger NEOs currently pose an impact threat and probably only a few dozen more of these large NEOs remain undiscovered.

The vast majority of NEOs are smaller than one kilometer, with the number of objects of a particular size increasing as their sizes decrease.

For example, there are expected to be about 15,000 NEOs that are about one-and-half football fields in size (460 feet, or 140 meters), and more than a million that are about one-third a football field in size (100 feet, or 30 meters).

A NEO hitting Earth would need to be about 100 feet (30 meters) or larger to cause significant devastation in populated areas.

Almost 30 percent of the 460-foot-sized NEOs have been found, but less than 1 percent of the 100-foot-sized NEOs have been detected.