The heated mill pond, or "hot pond," was invented around 1890. This innovation in Minnesota logging made it possible for logging companies to run their sawmills year-round.
Logging began on a large scale across the state of Minnesota in the mid-nineteenth century. At first, loggers cut trees only in winter, when it was easiest to move logs on sleds across the snow to nearby frozen waterways. The logs would sit on the waterways until spring, when the frozen water would melt and carry the logs downriver to water-powered sawmills.
At the mills, the floating logs were collected in designated areas called booms. The logs stayed there until they were cut into lumber and delivered to buyers. Minnesota timber was used locally for buildings and shipped out of state to fill construction needs elsewhere in the growing country.
By the late nineteenth century, railroads also were carrying logs to sawmills and steam power had joined water power as a way to drive saws in mills. These changes meant logging companies and mill owners no longer had to wait until the spring thaw to move wood downstream and cut it. They could move and cut year-round, without water power. However, it was difficult to cut frozen wood.
Hot ponds located right next to mill buildings solved this problem. Exhaust steam from the mill, or hot water from another source, was pumped into a standing body of water to keep it partially thawed all winter. Cut logs were piled into the heated water, where they thawed and softened. A shed or roof was often built over the hot pond, so that even the sections of log floating above water would be warmed and full logs could be sawn.
Logging in Minnesota reached its peak in the decades just before and after the turn of the twentieth century. Many of the sawmills built in the 1890s were designed with substantial hot ponds. One example, the hot pond at T.B. Walker's Red River Lumber Company mill in Akeley, Minnesota, was 125 feet wide and 500 feet long. It had a covering roof that measured 100 feet by 300 feet. Under the roof, 200,000 feet of logs could finish thawing before entering the mill. Other Minnesota mills had hot ponds with capacities of up to five million logs.
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"The steam log thawing apparatus." Mississippi Valley Lumberman 23, no. 2 (January 13, 1893): 1.
"T.B. Walker—Captain of Industry." Minneapolis Journal, November 29, 1903.