How do you know when a lake is safe to cross?

[John Dittli]

Well I wrote a two hour dissertation on the subject yesterday and seems that it has been lost in space, I’ll attempt a ClifNotes here. Having spent the last 50+ years crossing likely thousands of frozen lakes in the Sierra Nevada the following are my observations, key word; I’m no scientist or ice expert.

I’m going to skip talk of early season thin ice as I believe the OP is referring to late season snow covered ice. First and foremost to answer the question “how do I know when it’s safe?” The simple answer is, you don’t. Like evaluating snow slope stability, deep swift water crossings or any other situations that require risk assessment, there is often nothing ultimately safe about it, but rather, how dangerous might it be. This probably a good place to state that I have quite a fear of going into water over my head with skis on my feet and 40# on my back, watch Never Cry Wolf for an example. That said, I’m not adverse to risk.

Unlike hard, usually monolithic, early season ice, late season ice is usually more of a snow/water matrix that can be frozen solid or a slushy slurry if temps are warm. The white snowy ice is what I’m talking about here. Due to the relatively mild temps and deep snow of the Sierra I don’t believe lake ice ever gets more than a few feet thick. As feet of snow pile upon the ice it not only insulates it from cold air but forces the ice deeper into the water where it melts (water being above 32°). Think of an iceberg, only a very small fraction is above the water. This is also true for lake ice. Although settled snow is ~40-50% the density of ice, with buildup It keeps pushing the ice into the water. This is why I suppose I’ve never seen much more than a foot or two of snow on a lake even if there is 20’ on the shore.

As the season progresses, this white ice goes through a lot of differential melting. This can create both vertical and horizontal water filled voids within the ice. In fact one can, and I have, break through the top surface of ice into a foot of water before once again reaching supportive ice. Even if your not going to drown you may die of heart failure, it isn’t a pleasant experience.

So when do I cross a frozen lake? Well, I should point out that I’m rarely on a frozen lake sans skis and skis distribute weight far better than shoes though shoes are much better for swimming. White ice can be quite strong if well frozen or a non-supportive slush if not. I feel “comfortable” skiing across a lake on snow that shows no sign of ever being saturated by water. This indicates to me that the ice below has not melted enough for the above snowpack to become wet and if it can support the winters snow I figure it can support me. When water begins to rise in my ski tracks I feel considerably less comfortable. I also feel “comfortable” skiing across saturated snow that has been re-frozen in cold temperatures. In fact I have comfortably skied across advanced thaw of what I call blue margarita after a cold hard freeze; I’ve also gotten quite wet attempting the later when it wasn’t quite frozen. I stay off lakes that have a lot of visible sign of liquid surface water. It should also be noted that ice will be thinner along south facing islands and shorelines, inlets and outlets.

In closing, it is relatively unknown as to when a frozen lake is safe to cross, an avalanche path is safe to cross or a rushing stream is safe to cross. It’s always smart to choose the safest route which isn’t always the easiest.

[John Harper]

You'll find out soon enough if it isn't.

John

[c9h13no3]

The disparity in thoughtfulness of the two previous replies is like, big.

[John Harper]

The disparity in thoughtfulness of the two previous replies is like, big.

is there a forum rule against humor? Lighten up, Francis, you'll live longer.

John

[Harlen]

Love the Sierra writes:

... no one seems to cover when it is safe to cross a lake. In other words, how can you be absolutely sure that it is frozen solid enough to make a safe crossing?
Thanks so much to all of you experienced folks.

Me, I get right off as soon as I hear big cracking sounds. Safety first.

100_2803.JPG

I decided not to cross this lake-- too thin.

100_3091.JPG

We gave Tenaja Lake a miss this time too. Another rule of thumb: If you can still see the fish, do not ski across.

[Gogd]

Well I wrote a two hour dissertation on the subject yesterday and seems that it has been lost in space, I’ll attempt a ClifNotes here.

@ John Dittli
Thanks for sharing your experiences and sage observations. Provocative insight you share with us, wise Sierra Jedi! Comparing the risk assessment of ice activity with other activities was a good exercise. It got me thinking, why am I such a chicken about ice, when I am more comfortable assessing avalanche hazards?

At some level it boils down plain hubris. l've had snow travel and safety courses, I "know" how to read the snow, I've got this! That and I always stay at an Holiday Inn on the eve of my trips. On a more serious note, for me it comes down to risk management; rewards versus consequences. My friends scoff at how conservative I am about accepting avalanche risks. They give me **** for all the pits I dig - every time there is a significant elevation change, above and below ridges with suspect snow pillows (aren't all snow pillows suspect!?), changes in compass orientation of slopes, entering new basins, etc. Skiing the backcountry for me is primarily a mode of transportation, I ski to get in the mountains, not get into the mountains so I can ski. The BC is no place to ski off precipices and otherwise make believe you are in a Warren Miller flick - it is a veerryy long way to the ER. Thus I take on only what risk is necessary to get to Point B, and will take alternate routes or bug out altogether if the snow pit is talking to me. Yet I ski off into snow covered terrain, nevertheless. Ice skating and other over ice activities, however, are more for fun and convenience than a practicality, as far as my priorities go. So I have never knowingly traveled on ice in the BC That said, I have definitely done more than my share of honestly real stupid stuff, so it is not like I am condescending other's POV on the topic of risk assessment and travel on ice.

Ed

[Love the Sierra]

WOW @ John Ditti, thank you!!!
Fascinating answer!
Ed, I did not get the Holiday Inn joke.
As for me, I never “go” anyplace in the mountains. It is my vacation, my peace and well being. I go because it is fun, it is beautiful, and it is an awesome feeling to exhort every muscle in your body. Wherever I am, if I like it, that is my destination for the moment.
I guess that outlook comes from a life filled with a NEVER ENDING rushing from appointment to appointment, alarm to alarm.

[jmherrell]

Ice over water makes me extremely nervous. I avoid it whenever possible. One time skiing near Carson Pass in January, after traversing Elephants Back, I and two friends needed to cross Winnemucca Lake to get back to the trail. Because of its very exposed location right on the crest the ice was bare. The surface was covered with thousands of small re-frozen fractures. I crossed to the far side where an ice fisherman was boring a hole. He told me the ice was 14” thick. At no time did I realize that the ice was perfectly safe to cross.

For anyone who hasn’t heard this story, just a reminder that sometimes things go terribly wrong.
https://monocounty.ca.gov/sheriff/page/ ... ke-tragedy

[c9h13no3]

For anyone who hasn’t heard this story, just a reminder that sometimes things go terribly wrong.
https://monocounty.ca.gov/sheriff/page/ ... ke-tragedy

Yeah, Convict Lake is notorious for this problem due to this incident and others. Between being lower in elevation, and receiving less snow due to its easterly location, it is no sure bet to be solidly frozen.

[rlown]

It is called a life jacket. They weigh nothing. Take one when on sketchy ice.