May 2021 | Letter from the Directors

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Tuesday, May 25, 2021 

Emerging from the long isolation into the warmth of spring, the Broad Branch Road campus is abuzz with energy, literally.  The 17-year cicadas have emerged into the tree canopy.  Their calls to potential mates make the campus sound like the alien attack in the 1956 science fiction movie “Earth vs. the Flying Saucers”, which appropriately enough was set in Washington, D.C. 

Cicadas are not the only ones returning to campus.  Covid vaccinations will soon allow us to relax many of the campus access restrictions we have been operating under for the past 15 months.  We are already beginning to see the daily campus population increase.  We also are preparing to welcome a few new residents to campus when the Carnegie leadership moves to their new offices at BBR following the sale of the historic Carnegie building on P-Street.

Unlike the cicadas who go pretty much unnoticed during their time underground, EPL staff have been quite visible over the last year as they turn datasets acquired pre-pandemic into publications. As is typical of the work pursued by EPL scientists, the discoveries range from the deep Earth to distant stars.

What subducts, must go down

This figure shows a sample thermal model of a subduction zone, with the relatively cold (blue) oceanic plate sinking into the comparatively hot (red) mantle. Three regions of earthquakes (grey spheres) visible in the oceanic plate: "intermediate-depth" dehydration-related earthquakes occurring between ~70 and ~250 km, a region of reduced seismicity between ~250 and ~350 km, and the region of "deep" seismicity below 350 km that extends to ~700 km. Superdeep diamonds (blue octahedra) are known to crystallize from fluids released in this deep region as the oceanic plate warms by the heat from the surrounding mantle. Illustration by Steven Shirey, Peter van Keken, Lara Wagner, and Michael Walter/Carnegie Institution for Science

In the 1980s, former staff scientists Julie Morris, Fouad Tera, Lou Brown, and Selwyn Sacks helped prove that surface sediments carried down by subducting oceanic plates make it to the depth of magma genesis (~100-150 km) beneath the volcanoes that form at subduction zones — like those in the Cascades, Japan, and the Andes. Extending that discovery, EPL postdoc Peng Ni with staff scientists Steve Shirey and Anat Shahar tracked the impact of altered oceanic crust to depths approaching the upper mantle – lower mantle transition at 670 km depth. They found that the iron isotopic composition of minute iron metal inclusions contained in rare superdeep diamonds suggest their formation from fractions of oceanic crust that experienced severe hydrothermal alteration on the ocean floor before starting their descent into Earth. Their data provide more evidence for the efficiency of the continuing exchange of material between Earth’s surface and interior and its role in influencing whole planet dynamics.

In related work, Shirey with staff scientists Lara Wagner, Peter van Keken and Mike Walter showed that the transport of water carried to these depths and then released when hydrous phases transform into higher pressure anhydrous phases may be responsible for generating earthquakes that occur at depths of 400-700 km. At these depths rock is normally thought to be too weak to sustain the stress build-up needed for rock to fracture rapidly, creating an earthquake in the process. They reached this conclusion through a combination of data from inclusions within diamonds that derive from these depths, compiling a catalog of the precise locations of earthquakes in this depth range, and then comparing the thermal structure of the downgoing plate derived from geodynamic modeling with the phase diagrams for high-pressure hydrous phases.  The work involved geochemistry, seismology, computational geodynamics, and petrology in a show of the strength and promise of the type of multidisciplinary studies that are being pursued at EPL.

Earthquakes estimate magma viscosity

In May 2018, eruptive fissures opened and deposited lava within the Leilani Estates subdivision on the Island of Hawaii. Over 700 homes were destroyed, displacing more than 2000 people. By studying what happened, Carnegie's Diana Roman and her colleagues determined that the direction of the fault movements before and during the volcanic eruption could be used to estimate the viscosity of rising magma during periods of precursory unrest. (credit: B. Shiro, USGS)

Moving closer to Earth’s surface, staff scientist Diana Roman along with colleagues including former Geophysical Lab postdoc Don Dingwell were able to show that the nature of the earthquakes beneath a recent eruption of Kilauea in Hawaii could be used to estimate the viscosity of the magma underground. The viscosity of a magma is a key parameter in predicting the style of an impending eruption, particularly whether it is likely to be explosive or a passive effusion of magma. Passive eruptions such as the ongoing eruption of the new Geldingardalosgos volcano in Iceland can become enjoyable tourist sites, but even a passive eruption can be hazardous if you can’t get out of the way of the flowing lava fast enough. The ongoing evacuation and destruction of portions of the city of Goma that is being overrun by lava flows from the Nyiragongo volcano in the Republic of the Congo are a clear demonstration of the potential hazard presented even by a passively erupting volcano.

Flares of unusual size

Artist's conception of a violent stellar flare erupting on neighboring star, Proxima Centauri. The flare is the most powerful ever recorded from the star, and is giving scientists insight intonthe hunt for life in M dwarf star systems, many of which have unusually lively stars. Credit: NRAO/S. Dagnello

While lava flows reflect the considerable energy available in Earth’s interior, they pale in comparison to the sometimes violent outbursts from stars. Former postdoc Meredith Macgregor working with staff scientist Alycia Weinberger focused a wide range of telescopes on our nearest neighbor star, Proxima Centauri, in order to get observations of its flares across a wide range of wavelengths from radio to ultraviolet.  In the ultraviolet, they found the star increased in brightness by a factor of 14,000 over the span of a few seconds. These energetic flares do not bode well for the habitability of the planet orbiting Proxima Centauri that was discovered in 2016 by former postdoc Guillem Anglada-Escude in a study that also involved EPL staff scientist Paul Butler.

Lunar history in the lab    

Another discovery closer to home was the glove box used by staff at the Geophysical Laboratory (GL) in the initial studies of the lunar samples returned by Apollo 11.  The lunar samples stored in that glovebox were studied by Steve Haggerty, then a postdoc at the GL, to discover the mineral Armalcolite.  He named the mineral in honor of Neil Armstrong, Buzz Aldrin, and Michael Collins, the three Apollo 11 astronauts who collected and brought these samples back to Earth. 

Extraterrestrial examinations

Larry Nittler poses with 3D models of the asteroids Ryugu and Bennu.

Continuing our role in examining extraterrestrial objects, staff scientist Larry Nittler is expecting the delivery later this year of small samples of the Ryugu asteroid collected by the Japanese Hyabusa2 mission.  Who knows what mysteries those samples will reveal about the early Solar System?  We will in the not-too-distant future and we look forward to sharing these discoveries with you as soon as they are made. In the meantime, we invite you to attend our special Neighborhood Lecture event on Asteroid Day, June 30, 2021.  During his talk, Nittler will discuss how he uses these special space rocks to build the timeline of our Solar System's formation.

We can’t wait to see you there!

Rick Carlson and Mike Walter
Director and Deputy Director
Earth and Planets Laboratory