Peng, your not going to fall through 5″ of good clear ice.. but you can fall through 12″ of badly honeycombed(milky grey) ice. Clear ice is very strong, it loses some of its integrity as soon as you see any sign of air bubbles in the ice(very small bubbles). White ice is often frozen slush, and it can be pretty trong, but it can also be very weak.. never trust it, depend on the good clear ice underneath it. If its not good clear ice, its usually a pretty safe assumption the ice will have 1/2 the strength… So rather than 4″ of clear for walking/ice fishing, you should double that if its questionable ice.. or 8″.. if its damaged too bad, its not going to hold.
Keep the greatest respect for ice always.. that water is cold under it. Its best not to mess around with damaged ice at all. The lakes will be packing on ice slowly but surely, its not going to be long before there is plenty of good ice everywhere. Dont get adventurous, and know exactly what you are walking on.. test as you go. Bring picks, a chisel and test the thickness every couple feet if you have any doubt.
The cracking is due to freezing and flexing. Water expands as it freezes and it will crack to relieve the pressure. If the area is too large, it will create pressure heaves, and can also push ice up the banks pretty significantly. Ice also cracks when it flexes.. if your on a fair size or bigger lake on a windy day, or have a heavy object moving across the ice.. either will create a wave action and the ice will do some cracking. Snow piling up is heavy and can cause it also.
Popping ice doesnt bother me too much but it still makes me jump when a crack runs under/near me! If you want to get really freaked out, have it happen when your drilling a hole in thick ice(over 12″) and a crack goes through your hole while drilling it.. that will send you to a cardiologist.
