Weathering volcanoes

Accurate weather forecasts could help predict volcanic eruptions, according to British environmental scientists.

Researchers at the University of East Anglia working with colleagues at the Montserrat Volcano Observatory and the University of Maryland have discovered that intense rainfall can trigger volcanic dome collapse. This leads to a particular type of eruption in which a build-up of molten rock inside the side of the volcano becomes unstable and collapses spewing out lava, toxic gases, and rock.

The Soufrière Hills volcano in Montserrat with pyroclastic flow deposits visible on the left flank

The Soufrière Hills volcano in Montserrat with pyroclastic flow deposits visible on the left flank

The eruption on the Caribbean island of Montserrat in July last year coincided with the first heavy rainfall in seven months, explains team member Adrian Matthews. Within hours of the rainfall starting the volcanic dome collapsed. Matthews, a meteorologist, leads the research team with UEA volcanologist, Jenni Barclay. The scientists also found that two previous eruptions of the Montserrat volcano, Soufriere Hills, had also been preceded by heavy rainfall.

The researchers point out that one of the most dangerous aspects of volcanic dome collapse is the accompanying surge of searing hot rocks and boulders that are carried at high speed down the mountain on a bed of volcanic gases, the pyroclastic flow. Weather forecasts, the team says, used in conjunction with rainfall records might help make more accurate predictions of imminent volcanic activity and offer people who live in the shadow of active volcanoes an early warning of eruptions.

The devastated Montserrat capital of Plymouth under volcanic debris

The devastated Montserrat capital of Plymouth under volcanic debris

Montserrat had seven months with little rain and a period of sustained volcanic dome growth. Once the intense rain set in, it was only a matter of hours before the dome collapsed and pyroclastic flows started. The weather system that brought the rain could be seen in satellite images and was forecast 60 hours before the volcanic activity. The next step is to work out how the rainfall triggers the eruption, it may be the water being turned to steam and building up inside the dome, like a pressure cooker, adds Matthews.

Further reading

Geophys. Res. Lett., 29(13) (2002)
http://dx.doi.org/10.1029/2002GL014863

Soufriere Hills
http://www.geo.mtu.edu/volcanoes/west.indies/soufriere/

Suggested searches

Soufriere Hills volcano
Pyroclastic flows
Volcanoes

A closer look at a near miss

On the night of August 18, 2002, a chunk of rock several hundred metres across flew past the Earth at a distance of 530,000 kilometres – just a little further into space than the Moon. At the time, the British media were still reeling from the possibility that another asteroid was destined to collide with Earth in the year 2019.

However, a more down to Earth appraisal by Chris Benn, Sebastian Els, Tom Gregory, Roy Ostensen and Francisco Prada using the William Herschel Telescope on La Palma, Canary Islands, of NY40 while it was at an altitude of 750,000 kilometres is helping astronomers get a better understanding of these interplanetary objects.

The WHT is the most powerful optical/infrared telescope in the world (Credit: Nik Szymanek and Ian King)

The WHT is the most powerful optical/infrared telescope in the world (Credit: Nik Szymanek and Ian King)

NY40 was travelling at 65,000 kilometres per hour during its near miss but despite this, very high-quality images were obtained in the near-infrared end of the spectrum with a resolution of 0.11 seconds of arc (about 1/33,000 of a degree). This resolution is close to the theoretical limit of the Herschel telescope and sets an upper limit to the size of the asteroid of a mere 400 metres across at the time of the observations. Several observers have reported variations in the brightness of 2002 NY40. This suggests that the rock is highly elongated and tumbling through space. Further work is required to determine its orientation during different observations and so obtain a more accurate estimate of size and shape.

Sizing up asteroids will help astronomers understand their nature and formation history as well as the potential threat they pose. There is a small population of Near Earth Asteroids (NEOs) whose journeys around the sun occasionally approach or intersect the orbit of our planet. A direct intersection in time and space is thought to have occurred 65 million years ago wiping out the dinosaurs.

H-band (1.63 microns) image of asteroid 2002 NY40 taken on the night of August 17 to 18, 2002. (Credit: The ING NAOMI team)

H-band (1.63 microns) image of asteroid 2002 NY40 taken on the night of August 17 to 18, 2002. (Credit: The ING NAOMI team)

Fortunately, despite the media scare stories, the odds are stacked against an asteroid hitting the Earth in the near future. Close encounters with large Near Earth Asteroids, like 2002 NY40, do happen every fifty years or so. NEA 2001 CU11 passed just outside the Moon’s orbit on the 31st of August 1925 but it was not observed at the time. Indeed, it was not actually discovered until 77 years later.

The NAOMI Adaptive Optics system at the Nasmyth focus of the William Herschel Telescope (Credit: The NAOMI team)

The NAOMI Adaptive Optics system at the Nasmyth focus of the William Herschel Telescope (Credit: The NAOMI team)

NAOMI was created by researchers at the University of Durham and the UK Astronomy Technology Centre. It incorporates a system of fast-moving mirror elements, which correct in real-time for the defocusing of stars caused by the Earth’s turbulent atmosphere – it compensates for twinkling, in other words!

Further reading

Near Earth objects
http://neo.jpl.nasa.gov/news/

Deep impact!
http://www.space.com/scienceastronomy/planetearth/deep_impact_991228.html

NAOMI
http://www.roe.ac.uk/atc/projects/naomi/

UK Astronomy Technology Centre
http://www.roe.ac.uk/ukatc/

Suggested searches

Near Earth object
Asteroids

The physics of chemical waves and disease

Waves come and go, but a study of chemical waves by US physicists could improve our understanding of how pathogens flow around the body and how mutant genes spread through invading populations of viruses. The research might ultimately help medicine find a way to control the rate of viral mutation and so block the spread of retroviruses, such as HIV, which rely on mutations to overcome the body’s immune defences.

Boyd Edwards of West Virginia University has analysed the motion of chemical wavefronts through a filled tube with a fluid moving in the opposite direction through the tube. Intriguingly, he discovered that the chemical wavefront is not slowed by the liquid, which one would imagine contravenes at least one of the laws of nature. We’ve learned chemical waves are like pedestrians in a hurry, explains Edwards. Head winds don’t slow them down but may bend them out of shape. Tail winds, on the other hand, speed them along.

Edwards analysis - going against the flow

Edwards analysis – going against the flow

Edwards has previously published research on the critical wavelength needed for a river to meander and the dynamics of falling raindrops, but this current research focuses on a more esoteric phenomenon: chemical waves.

Chemical waves thrive on the diffusion and mixing of interacting ingredients. One of the most beautiful examples is the Belousov-Zhabotinsky (BZ) (BZ Ref 1 and BZ Ref 2) reaction in which a wave of changing colour sweeps through the reaction mixture. The reaction involves the interchange of a chemical by a reduction-oxidation (redox) reaction. Each step generates a catalyst that speeds up the counter reaction. Therefore, as the reduction proceeds, for instance, it produces more and more catalyst to speed up the oxidation and vice versa. The reduced state reaction is red while the oxidised state is a pale brown.

BZ reaction

BZ reaction

It takes just a tiny fluctuation in the ingredients favourable to either the reduction or the oxidation to trigger a chain of reactive events that spread outwards from the centre like ripples on a pool. The BZ reaction left unstirred produces striking geometric growth patterns. Such patterns are reminiscent of animal patterns, such as those of water snails, leopards and zebras and indeed chemical waves were first implicated in how the leopard got its spots by Cambridge mathematician and cryptography expert Alan Turing (Turing homepage and Turing reference). As one reagent diffuses and is used up, it meets its counterpart so the reaction product diffuses ‘behind’ it and meets with its counterpart propagating the counter-reaction.

The BZ reactions and its chemical cousins bring together the reaction between ingredients and how they diffuse through the reaction mixture. Edwards has used trusted fluid mechanics equations to look at a simpler version of the BZ reaction that also involves a moving chemical wavefront. He predicted that a chemical wave front moving through a tube filled with fluid moving in the opposite direction would develop a trailing spike at the centre of the tube. The spike consumes just enough extra fluid to compensate for the flow, thereby allowing the wave front to travel at its usual speed. In contrast, a chemical wave moving in the same direction as the flow is carried along by the flow, and travels faster than one would intuitively anticipate.

Edwards says that experiments are already under way at WVU to test his predictions, while doctoral student Robert Spangler is investigating the deeper theoretical implications.

Research in chemical waves may prove to be useful in medicine, since chemical waves are similar to biological waves found in the body, Edwards explains. One example is electrical waves that cause the heart muscle to contract. Research on chemical waves might lead to the design of pacemakers which can better respond to life-threatening fibrillation. The spread of pathogens, toxins and poisons through the bloodstream might also be investigated using the fundamentals of the study.

Edwards confesses to not being an expert in genetic mutation and that is research is at a scientifically fundamental level, but he says, there may indeed be eventual ties to these biological areas. The research may also have something to say about the molecular diffusion of a pathogen into uninfected blood in the bloodstream. Non-uniform fluid flow (advection) can increase the diffusion rate of a pathogen, as some portions of the chemical wavefront are carried forward faster than others by the nonuniform fluid flow.

Further reading

Phys. Rev. Lett. 89, 104501 (2002)
http://dx.doi.org/10.1103/PhysRevLett.89.104501

Boyd Edwards
http://physics.wvu.edu/people/boyd_edwards

Turing homepage
http://www.turing.org.uk/

Turing reference
http://www.ma.hw.ac.uk/~painter/research/pigmentation/fish.html

Suggested searches

Belousov Zhabotinsky reaction
Fluid mechanics
Redox reactions