Though it's barely the beginning of autumn, scientists at the University of Toronto are one step closer to explaining why winter's icicles form with Michelin Man-like ripples on their elongated shapes.
This is a natural ripply icicle, collected to measure water composition.
Credit: Stephen Morris
Experimental physicist Stephen Morris and PhD candidate Antony Szu-Han Chen were spurred to investigate by the ripples that appear around the circumference of icicles that occur naturally. It has been theorized that the ripples are the result of surface tension effects in the thin water film that flows over the ice as it forms. Their investigation revealed that the actual culprit is salt.
"Nobody has systematically investigated what causes the ripples so we began growing them in the lab," said Chen, lead author of a paper published online this week in New Journal of Physics. Accounting for key factors that influence the shape of an icicle as it forms in nature – ambient temperature, flow rate of water and the motion of the air surrounding it – the researchers experimented with the composition of the source water.
"We had already tried Toronto tap water and found that it formed ripply laboratory icicles, when distilled water didn't," said Morris. "We also confirmed that melted rippled icicles taken from Toronto garages were very slightly salty, so that's what led us to pursue the composition factor."
Using pure distilled water, distilled water with small quantities of sodium chloride added, and Toronto tap water – which contains sodium chloride as well as many other impurities – they produced 67 samples grown under a broad range of conditions. The evolution of the icicle shapes over time was acquired from digital images using detection of their edges, which were then analyzed with computer image processing.
Ripple growth was not observed on distilled water icicles, whereas saltier icicles showed clear ripples that appear in a patchy way and sometimes grew as large as a few millimetres. The ripples were seen to move slowly upward during the icicle growth, though the researchers note that both the speed and direction of the ripple motion could vary depending on the concentration of dissolved salt.
Morris and Chen found that ripples only became apparent at the remarkably low salinity of the water with 20 mg of salt per litre. This level, in fact, is a considerably lower level of impurity than found in common tap water.
"We even added a non-ionic ingredient to the distilled water to reduce the surface tension of the thin film of water flowing over the icicle, and it didn't produce ripples," said Chen. "Instead, ripples emerge only on icicles grown from water with dissolved ionic impurities."
"Our motivation is pure curiosity about natural patterns, but the study of ice growth has serious applications, including ice accumulation on airplanes, ships and power lines," said Morris. "This result is totally unexpected, not just by us before we did this, but by theorists and experimentalists in our field who study ice dynamics and pattern formation."
"No theory accounts for the effect of salt, so the shape of icicles and the reason for their ripples are still mysteries. Except we now know that a little salt is required in the recipe."
The findings are reported in the paper "On the origin and evolution of icicle ripples". The research is supported by funding from the Natural Sciences and Engineering Research Council of Canada.
Note to media: Contact Sean Bettam at firstname.lastname@example.org for images and videos of the research described here.
MEDIA CONTACTS:Stephen Morris
Sean Bettam | EurekAlert!
Writing and deleting magnets with lasers
19.04.2018 | Helmholtz-Zentrum Dresden-Rossendorf
Ultrafast electron oscillation and dephasing monitored by attosecond light source
19.04.2018 | Yokohama National University
Study published in the journal ACS Applied Materials & Interfaces is the outcome of an international effort that included teams from Dresden and Berlin in Germany, and the US.
Scientists at the Helmholtz-Zentrum Dresden-Rossendorf (HZDR) together with colleagues from the Helmholtz-Zentrum Berlin (HZB) and the University of Virginia...
Novel highly efficient and brilliant gamma-ray source: Based on model calculations, physicists of the Max PIanck Institute for Nuclear Physics in Heidelberg propose a novel method for an efficient high-brilliance gamma-ray source. A giant collimated gamma-ray pulse is generated from the interaction of a dense ultra-relativistic electron beam with a thin solid conductor. Energetic gamma-rays are copiously produced as the electron beam splits into filaments while propagating across the conductor. The resulting gamma-ray energy and flux enable novel experiments in nuclear and fundamental physics.
The typical wavelength of light interacting with an object of the microcosm scales with the size of this object. For atoms, this ranges from visible light to...
Stable joint cartilage can be produced from adult stem cells originating from bone marrow. This is made possible by inducing specific molecular processes occurring during embryonic cartilage formation, as researchers from the University and University Hospital of Basel report in the scientific journal PNAS.
Certain mesenchymal stem/stromal cells from the bone marrow of adults are considered extremely promising for skeletal tissue regeneration. These adult stem...
In the fight against cancer, scientists are developing new drugs to hit tumor cells at so far unused weak points. Such a “sore spot” is the protein complex...
In an article that appears in the journal “Review of Modern Physics”, researchers at the Laboratory for Attosecond Physics (LAP) assess the current state of the field of ultrafast physics and consider its implications for future technologies.
Physicists can now control light in both time and space with hitherto unimagined precision. This is particularly true for the ability to generate ultrashort...
13.04.2018 | Event News
12.04.2018 | Event News
09.04.2018 | Event News
19.04.2018 | Materials Sciences
19.04.2018 | Physics and Astronomy
19.04.2018 | Physics and Astronomy