I would like to compliment Dr. Revettas report in the Watertown Daily Times on Jan. 6 regarding the cold-weather thumping sounds that north country residents have been experiencing.
The recent ice storm left a thickness of interlayered ice and sleet pellets both on the ground and on the roofs of homes creating a frozen crust as rigid as ice on a lake. As lake ice forms, it expands, letting out a sharp report resulting in pressure ridges and internal cracks. Similarly, ice storm ice on a roof that is warmed during the day expands as the temperature drops at night and produces a thunderous house-shaking boom.
In my backyard, I have seen pressure ridges in the ice crust, and I have heard an audible component as they form. Also, bare water-saturated ground will produce noisy frost-heaves as the temperature drops.
John T. Johnson