Aerial view of the research study region in the Argentine Andes. Credit: J.R. Slosson
The Earth is constantly subjected to an overwhelming increase of cosmic rays– subatomic particles that are undetected to the human eye and originate from sources such as the sun and supernova explosions. As these high-energy cosmic rays, which have actually taken a trip country miles, make their method into the Earths atmosphere, they hit atoms and activate a domino effect of secondary cosmic rays.
When the secondary cosmic rays reach the upper meters of the Earths surface, they transform elements within minerals, such as oxygen, into rare radioisotopes referred to as “cosmogenic radionuclides”, including beryllium-10 (Be-10) and carbon-14 (C-14). Researchers can evaluate the changes in the concentrations of these nuclides to determine the length of time that rocks have actually been exposed on the Earths surface. This supplies researchers with valuable insights into planetary procedures, such as erosion rates, with simply a single kg of river sand.
Gregory Hoke, the Jessie Page Heroy Professor and department chair of Earth and ecological sciences at Syracuse Universitys College of Arts and Sciences, J.R. Slosson, a postdoctoral researcher at UMass Amherst who received a Ph.D. from Syracuse University, and Nat Lifton, associate teacher of Earth, planetary and atmospheric sciences at Purdue University, just recently co-authored a study published in Geophysical Research Letters evaluating cosmogenic radionuclides in samples from the Argentine Andes.
The objective of the project was to record the quantity of time product resides on the hillslopes in the Andes Mountains relative to the overall erosion rate of the river basin. This info is vital to helping scientists determine landslide dangers and understand how environment change will impact the dynamics of product transport on hillslopes as regions get wetter or drier.
History Written in the Sand
To identify disintegration rates, the group acquired samples of river sand gathered at the foot of the eastern flank of the Andes Mountains in the Mendoza and San Juan provinces, situated in west-central Argentina. The river sand is to be an agent, well-mixed sample of the entire catchment (or runoff location) upstream of where the sample was gathered. In Hokes laboratory at Syracuse University, the sand was treated to isolate pure quartz from the other minerals present in the sample.
The researchers use pure quartz since it is an optimal source for Be-10 and C-14. Splits of pure quartz were sent to the University at Buffalo and Liftons laboratory where beryllium and carbon were extracted, respectively. Subsequent measurements of C-14 were carried out at Purdue Universitys PRIME Lab and Be-10 was evaluated at Lawrence Livermore National Laboratory to determine the concentrations of each radionuclide.
A Tale of Talus
The highest non-volcanic peaks in the Andes are located in between Santiago, Chile, and Mendoza, Argentina. The river basins that drain the high Andes cover 5,000 m (16,500 ft) in elevation and their hillslopes are lined with accumulations of rocky debris called talus and scree.
Because Be-10 and C-14 are produced proportionally however decay at greatly different rates, the cosmogenic radionuclide concentrations within a sample reveal the rate at which sediment is produced from bare rock surface areas (Be-10) and the time it takes to travel down hillslopes through landslides (C-14). As sediment is set in motion and buried through land sliding, the rate of production of both isotopes decreases, however since C-14 decomposes 1,000 times faster than Be-10, their proportionality changes quickly. This modification in proportion permitted the authors to apply a statistical model to determine the average period of time it takes material to take a trip down talus slopes.
EES professor Gregory Hoke co-authored a research study investigating how long product lives on hillslopes in the Andes Mountains.
According to author Gregory Hoke, this is among the first studies to use the mix of Be-10 and C-14 to reveal the long-lasting typical rate of sediment generation and the time and procedure it requires to move down to and through the rivers, giving a broader photo of the elements included.
” Previously, weve relied almost specifically on Be-10 and sediment concentration measurements made at river gauge stations to approximate typical erosion rates,” notes Hoke. “What attracted us to study these catchments with C-14 was the contract of gauge and Be-10 information. We expected to see the 2 isotopes and evaluate data yield the same rates and demonstrate that mountain disintegration was occurring at a consistent state.”
While the concentration of Be-10 came back as expected over the long timescale, they found that C-14 was much lower than expected, meaning that sediments eroded from the high mountain watersheds and were shielded from cosmic rays for a minimum of 7 to 15 thousand years. The authors describe that temporary storage in talus slopes best explains the lower concentration of C-14 relative to Be-10.
” This research study reveals that it is possible to fill an essential gap in the observational timescale utilizing the C-14/ Be-10 set that brings to life what truly occurs on the hillslopes,” says Hoke.
With the threat that landslides posture to humans and infrastructure, J.R. Slosson states their results indicate that C-14 can be significant in unraveling sediment transport characteristics going forward, and possibly assist forecast where future landslides may occur. He explains, “making use of C-14 along with Be-10 provides a brand-new window into the complexity of sediment transportation in mountain settings and can provide a background for evaluating modern changes in earth surface procedures.”
The research study was funded by the National Science Foundation, the Geological Society of America, the Syracuse University Education Model Program on Water-Energy Research, and the Syracuse University Research Excellence Doctoral Funding program.
When the secondary cosmic rays reach the topmost meters of the Earths surface, they change elements within minerals, such as oxygen, into uncommon radioisotopes understood as “cosmogenic radionuclides”, including beryllium-10 (Be-10) and carbon-14 (C-14). Subsequent measurements of C-14 were performed at Purdue Universitys PRIME Lab and Be-10 was evaluated at Lawrence Livermore National Laboratory to figure out the concentrations of each radionuclide.
Since Be-10 and C-14 are produced proportionally however decay at vastly different rates, the cosmogenic radionuclide concentrations within a sample expose the rate at which sediment is produced from bare rock surface areas (Be-10) and the time it takes to travel down hillslopes through landslides (C-14). As sediment is activated and buried through land sliding, the rate of production of both isotopes reduces, but because C-14 decays 1,000 times faster than Be-10, their proportionality changes rapidly. “What attracted us to study these catchments with C-14 was the contract of gauge and Be-10 data.
