Know When It's Safe to be on the Ice
I was wondering the same about Ice thickness; I found an article stating the middle the pond is the last to freeze because sunlight focuses;
Is Ice Thicker in the Middle of a Lake? Surprising Facts You Never …
When I was a young kid, our family lived in Cincinnati, OH for a few years. Across the street and about 100 yards in, was a small lake. The people who owned the lake were generous and mindful. When the ice formed, they'd shoot a .22 into it and if the ice held to their satisfaction, we were allowed to ice-skate and sled across it. As long as we lived there, there was never an accident or incident. Spent many happy hours on the ice on that lake!
When I lived in Alton NH a member of the Alton Bay Flying Club and had my own Cessna 172, in February President's weekend we plowed a runway on the ice and had fly-ins. The only FAA sanctioned ice runway in the US at that time. Planes came from all over to experience it including twin engines and as far way as VA & MI.. The stores ran out of goodies. The gazebo in the middle of Alton Bay was the command center. I parked many airplanes. There were a couple of skidding accidents were the pilot met with a snow bank.
Taxiing around and parking the planes around the ice fishing shacks and staying between the snow banks was interesting.
If a Google search for the Alton Bay Winter fly-in was done, many pilots posted a video showing what it's like to land. This is unique in NE. OFA or Yankee Magazine should do a story about it.
As the snow was plowed off the ice, it exposed the ice to freezing temperatures making the ice thicker. The benefit of thick ice.
I realize that my fears are probably completely ridiculous, but I live right on the banks of a river and my city curates walking, skating, and cross-country ski trails on it. I assume that they're measuring, and I frequently see lightweight vehicles driving down the skating trail (which is in the center and almost certainly where the ice would be thinnest) to clear off the snow, so I know that the ice is thick enough to support the weight of that vehicle. Even so, sometimes when I'm walking or skating, the ice will make cracking sounds that I find extremely alarming. It's been VERY cold here lately (like, -30 Celsius and lower), so I also know intellectually that it's almost certainly too cold for the ice to be in any danger of melting, yet the cracking sounds scare me. Is there anything you could tell me to reassure me that this is normal or something? The river itself is shallow, especially in winter (maybe 20' at the deepest, more like 8' at the shallowest), and there are places where you can see that the ice is at least a foot thick. All the same, I nearly have a heart attack every time I walk over a spot and it starts making those cracking sounds. Reassure me??
At those Temps for a couple weeks you are as safe as ice gets the cracking sounds are likely the pressure of new ice forming or barely shifting from you walking on. Often sound like an electrical type sound of dune dune dune. Happens all the time when I am fishing on ice. But still is spooky no matter how many times I hear it.
Those are just pressure cracks that you hear basically it is making the ice stronger. You are sick but be very careful with ice on a river, as there is always moving water underneath and may not always need to see this even with extreme cold temperatures.
River ice is more dangerous than flat water ice. In addition to the risks mentioned in other replies (especially flow), river water can and commonly does change levels after freezing. When cold weather continues for a long time, streamflow diminishes, the water level falls, and a shelf of ice can be left hanging in mid-air.
Water level in a river may also be controlled by upstream or downstream dam effects that you are probably not be aware of. When I read about people falling through ice, it is usually on a river. I have fallen through ice once, while snowshoeing over a flowage in a marsh. It was only waist deep, but the bottom was very slippery, and the current threatened to pull me under the ice. Also, my snowshoes got entangled in vegetation. Personally, I only go on river ice if I can walk along recent tire tracks! BTW, if you ever do hear lots of cracking as you step forward and feel it give, immediately lay down flat on the ice and creep back in the direction you came from!