As described in a study published in Physical Review E, by growing icicles from water samples with different contaminants like sodium chloride (salt), dextrose (sugar) and fluorescent dye, the researchers discovered that water impurities become entrapped within icicles as they form and subsequently create chevron patterns that contribute to a ripple effect around their circumferences.

Here is a link to the full article in UofT's A&S: https://www.artsci.utoronto.ca/news/more-profound-appreciation-complexity-natural-ice-formations