Thermistors on Turtle Mountain

What is a Thermistor?

A thermistor is an electrical probe to measure temperature. It is made of various semiconductor materials whose electrical resistance varies as a function of temperature. Thermistors can be arranged in a series on a cable to measure profiles of temperature within the ground.

Thermistors on Turtle Mountain

Borehole drilling. Click on image to enlarge.

To complement the weather station data with subsurface information, we had a thermistor string installed in the South Peak borehole in early October 2004. Because we were unsuccessful at installing a thermistor string 55 metres deep into the borehole, we installed a shorter string with sensors at depths of 2.1, 5.2, 8.2, 11.3, 14.3 and 17.3 metres (thermistors Th_6 to Th_1, respectively). A seventh sensor (Th_7) is above ground in the protective conduit connecting the thermistor cable to the data-gathering equipment in the borehole enclosure. Since these installations are below ground, there are no photos.

The datalogger in the South Peak borehole enclosure takes hourly temperature measurements at each of the thermistors, and then transmits the measurements to the provincial building at Blairmore. This information is sent to the Frank Slide Interpretive Centre through radio telemetry.

Rock temperature shows the same general trend as air temperature, but is more subdued (lower maximum and higher minimum readings) with a time lag of about 12 hours relative to significant changes in air temperature.

Seasonal temperature changes penetrate only about 15 metres into the slope (Th-2) and are negligible below that depth, with significant temperature variations measured down to a depth of 8.2 metres (Th-4). On the other hand, daily temperature variations are measurable only about 4 metres into the slope.

Typical rock temperature variation with depth at the south peak of Turtle Mountain a) during winter and summer, and b) at two extreme air temperature drops. Click on images to enlarge.