I just finished reading the full thread. I agree with you @Fucklechuck and the majority of pp.
They put those children at serious risk, are trivialising the actual risk and regarding themselves or the leader of this activity as having a much higher level of expertise than they actually have which is dangerous in and of itself.
He estimates the thickness of the ice by the estimated depth of the lake and the length of time being below 0 degrees. According to experts the thickness of the ice will be determined by many factors including the area of exposed water and sediment etc.
For anyone who is interested
I thought I’d post an article that does have expert information about how to recognise ice that is safe to walk on. And after reading this there is a lot that could be learned from observation from the shoreline and not walking on the ice and not by feel.
www.theweathernetwork.com/ca/amp/news/article/how-thick-does-ice-have-to-get-to-be-safe-to-walk-or-skate-on
Is it safe? How thick does ice need to be to walk or skate on?
Scott Sutherland
Meteorologist/Science Writer
Monday, 21 November 2022 8:37 PM
Pay close attention to the colour of ice before you step out onto it!
We can do a few things to tell the thickness of the ice on any body of water.
We can cut or drill down into the ice to take direct measurements. This is definitely the fastest way and the one that involves the least amount of guessing. There's one problem, though: you actually need to walk out onto the ice to do this. So, you could immediately be putting yourself in danger if the ice isn't thick enough to support your weight.
We can do a lot of physics and mathematics to determine the exact freezing rate of that particular body of water and exactly how long the water has been exposed to below freezing temperatures, and the effects of wind-chill. This process is quite complicated, however. It can easily vary from body of water to body of water, depending on the area of the exposed water surface, the depth of the water, the presence of moving water or currents, and the exact contents of the water, such as sediments, salt, chemicals, etc.
There is one easy way to get a reasonable estimate of the ice thickness, which can be performed safely from the shoreline, without needing to get out a calculator. We can look at the ice colour.
The strongest and safest colour of ice is either blue or black. This is the ice that forms as the surface of the lake or pond directly freezes in cold weather. As a result, it is very dense. This is where the ice thicknesses mentioned by the Canadian Red Cross come in. Blue ice must be at least 15 cm thick to be safe to walk on. If a group of people are venturing out onto it, 20 cm thick is safe. At least 25 cm thick is best for snowmobiling, and it should be even thicker for bigger vehicles — 30 cm or more for cars and light trucks, and 40-50 cm thick for anything larger.
(The actual image didn’t copy on Mumsnet)
Blue-Ice
This is what a frozen lake or pond should look like if you plan on skating on it. The dark blue ice is dense, strong, and the safest ice to venture out onto.
If the ice is opaque white, it can appear safe, but that is not necessarily the case.
White ice or 'snow ice' is white because it forms when a layer of wet snow freezes on top of blue ice that has already formed. Snow layers contain a lot of air, which end up as air bubbles trapped in the ice structure. While it can be reasonably thick, the presence of these air bubbles weakens the ice, so it may not be safe to walk on. It is still the thickness of the blue ice underneath that determines, ultimately, whether it is safe to stand on.
Be extremely cautious about venturing out onto white ice. This is especially true if there have been recent swings between warm and cold weather or if there is moving water under the ice. Also, if there is a layer of fresh snow atop the ice, the snow may be concealing thin ice underneath. Snow on top of ice also acts as insulation, trapping heat that will prevent the blue ice from growing thicker.