What is black ice--and why is it slippery?

  • Black ice is relatively smooth, hard, and clear.
  • Packed snow eventually turns to black ice, especially when it rains, or when there's a thaw, followed by freeze.
  • You must completely remove packed snow if you want to prevent ice buildup.
  • Black ice is most slippery when water is present.   Then it can be very dangerous.  Applying sand to ice greatly improves traction.
Black ice on the roads is what sends cars spinning out of control.  On sidewalks with black ice, pedestrians fall without warning.  So what is "black ice," and how does it form?

This "black ice" formed by freezing of meltwater.  It looks bright because it's reflecting the sunset.

Black ice is no different from ordinary ice--except that it's more compact and has a smoother surface.  Here's how snow turns to black ice.


How to prevent sidewalk ice--without salt

Use the sun instead of salt!

Key ideas...
  • Prevent packing during snowfall by clearing a narrow lane--people walk there, preventing packing elsewhere.
  • Clear to full width by noon of the day following snowfall.
  • Scrape remaining packed snow so light gets through to the pavement.
  • Let the sun evaporate the rest (ice can evaporate without melting).
  • Touch up daily--before leaving for work.
Removing packed snow prevents ice


Clear sidewalk snow without salt

Prevent snow from packing down...
because packed snow turns to hard ice in a few days.

Snow blowers make things worse, because they leave a layer of packed snow.

Use a shovel with a sharp edge (or an ice scraper) to remove packed snow. The sooner you remove it, the less the ice sticks to pavement.

Shovel a narrow lane as soon as you can. People will walk there, and won't pack snow on the unshoveled portion.

Now use solar power to melt the rest! 
To disappear, ice (or packed snow) does not need to melt. It can go directly from solid to water vapor, even at temperatures below zero! It's called "sublimation."

Ice does require energy to vanish without melting. You have to scrape the snow thin enough so light energy will penetrate to the pavement. Even with thin clouds on cold days, enough sunlight penetrates to make a difference. The ice will disappear in a few days, depending on temperature and sun. Touch it up before you leave for work... the sun will do the rest.

To prevent icy patches from forming when it warms up, clear to the edge of the sidewalk between snowfalls. This way, any meltwater sinks into the ground at the pavement's edge. You don't get icy puddles on the sidewalk.

With more pavement exposed, the sidewalk area gets warmer, helping to prevent new ice--and the next snowfall is easier if the whole sidewalk has been cleared.

You have to clear your sidewalk, but you don't have to shovel your driveway, at least not right away.

Work in stages to avoid fatigue, resting between. First the central strip of the sidewalk. Then scrape packed snow. Then enlarge the width of the path. Finally, clear to the grass and chip any remaining ice.

Check the weather report. If it's going to warm up, no worry to clear snow. If a long period of cold weather is coming, be careful to prevent packed snow. Salt doesn't melt ice at temperatures below about 15F, but the sun does!

Even on hills or steps, you don't need salt. Sand works very well. You can find it in city barrels at street corners. You can buy Yaktrax to make your shoes slip-proof.

Hope this helps! HAPPY SOLAR SHOVELING !


Lecture by top expert on monarch butterflies

A lecture by Dr. Karen Oberhauser.
October 18, 7 p.m.-8:30 p.m. at the UW Arboretum Visitor Center, 1207 Seminole Highway.
"Oberhauser, one of the nation's top monarch conservation
biologists, will describe the amazing biology of migratory monarch
populations, and the work of citizens and scientists in
documenting monarch numbers at all stages of their migratory
Sponsored by the Madison Audubon Society & the WI Chapter of the Society for Conservation Biology.


Does road salt make winter driving safer?

Given the lack of progress since Madison first tried to reduce road salt use, it's time to look for new ways of viewing the problem.

As soon as a conversation about salt begins, the subject of winter road safety comes up.  Road safety seems to override any other argument.

But does salt really make winter driving safer?  We can refine this question to ask... "Do the obvious safety benefits of salt outweigh the enormous economic and environmental damage caused by salt?"

"Outweigh" implies that we have to measure--to quantify--both the benefits and costs of salt.

An obvious starter...  Are there any highway accidents actually caused by salt?

A bridge collapses


How road salt led to poisoned water in Flint, MI

It's time to recognize that spreading too much salt in Madison could have dangerous and unforeseen consequences.

In Flint, MI, road salt played a role in poisoning the public water supply.  When Flint switched the source of its water from Lake Huron to the Flint River, salt in the city's water soared from from 11.4 mg/l to 92 mg/l.  Salt in the river came largely from overuse of de-icing salt on roads.

Salt (chloride) is extremely corrosive.  It caused Flint's lead pipes to corrode, releasing lead that can cause brain damage in children.  At the home of Lee-Ann Walters and her 3-year-old son, average lead levels were measured at 2,000 ppb, sometimes exceeding the EPA criterion for "toxic waste."

Despite the increase in salt, the city did not add a corrosion inhibitor* to the water as many cities do. So both iron and lead pipes corroded, resulting in lead poisoning of many children.

Could Flint's poisoned water happen here?

Our situation is different, because Madison has replaced all its lead plumbing.  But three of Madion's shallower wells are becoming contaminated with salt (up to 37 mg/l in 2013).   The level of chloride in Lake Wingra is 130 mg/l and headed upward.  MG&E has been pumping millions of gallons of salty water into the ground with the Odana Project.

Even without lead pipes, chloride in city water can cause big problems.  The chloride corrodes iron pipes and water mains.  Flint has reported increased leaks--the corrosive water will cost millions of dollars in damage to pipes.  And when iron pipes corrode, they use up chlorine added to the water to kill bacteria.  That's why Flint had bacteria in their water--chlorine was rapidly used up after leaving the wells, leaving the water reaching consumers unprotected.

Madison's older water mains can rust from the inside and the outside. Chloride in both tap water and groundwater has been steadily increasing. Madison needs to replace half of its 400 miles of pipe.  By 2020, the annual cost of replacing or relining Madison's water pipes will be $12.7 million.

While the US does not consider chloride to be a pollutant, Canada does consider it "toxic," based on potential damage to the environment.  How long before Madison's salt reaches crisis levels? We already know salt causes billions of dollars in property damage, rusting autos, corroding bridges, and weakened parking ramps.  Now Flint demonstrates salt can have dire and unpredictable health consequences.  Our leaders should lead by taking decisive action to limit salt. 

Chloride in Madison's tapwater See p. 3. The median level of chloride in Madison's wells is 24 mg/l, ranging from 2.2 to 106 (2013).

* A corrosion inhibitor has been rejected by Madison's Water Utility, because it contains phosphorus which would also harm our lakes and streams.


Monarchs threatened by climate change in their wintering areas


Monarch butterflies roost in huge numbers during the winter only in oyamel fur trees in the mountains of central Mexico.  The fur's dense foliage provides insulation from freezing temperatures. And unlike other trees, monarchs can easily cling to the fir's tiny needles with their claws.

But as temperatures rise with global warming, oyamel furs won't be able to survive where they are growing now.  People will have to plant the oyamels at higher elevations, so the butterfly reserves will be ready for changed conditions.

That's just what Mexican conservationists are planning for now.

Find out more here.
Photos of my trip to the wintering areas in 2015.