You may have heard that on June 30th the official temperature at the headquarters of Death Valley National Park, Furnace Creek, was 129.2 Fahrenheit, making it the hottest June temperature measured on Earth in history. But that was hardly the hottest temperature in Death Valley that day, as the above U.S. Geological Survey (USGS) images reveal and my past experience as a ranger there tells me.

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The false color image shows the ground temperatures on that very hot day. It was taken by the Thermal Infrared Sensor on the USGS’s Landsat 8 satellite. The lighter the color, the hotter the ground was in this image. The natural color view is in infrared and collected by the same satellite on the same day by the Operational Land Imager. One of the things that the images show is that, generally speaking, the higher you go, the cooler it was that day, which makes sense. Or does it?

Turns out it’s not as simple as elevation. The type of ground also matters and there are some very exotic kinds of ground in Death Valley. For instance, notice the area to the southwest (lower left) of Furnace Creek — the natural color image shows very bright ground that is actually cooler (darker) in the thermal image. That is because this area is lower than Furnace Creek and has no plants. Furnace Creek is darker in both images because of its trees and other plants. The cooler ground is made of highly reflective salt: miles and miles of salt crystals at the bottom of what was, tens of thousands of years ago, a vast inland sea with no outlet.

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Now look at the dark brown (in natural light) alluvial fans coming out of the mountains on either side of the salt. They are much hotter (brighter in the thermal image), while being higher in elevation. These areas are made of a collection of darker rocks that have eroded from the mountains. The darker rocks absorb more sunlight, getting a lot hotter.

While surface temperatures are certainly different from air temperatures, the heat coming from the ground does play a big role in heating up the air a few feet off the ground where the official thermometers are typically kept. And if there are trees nearby shading the ground, as there are near the Furnace Creek thermometer station, that cools things as well.

All this suggests that the air temperature out on those alluvial fans was a lot more than 129.2 Fahrenheit recorded in the leafy Furnace Creek area. So while that’s a nice record, it’s hardly as hot as it got that brutal day. Maybe it was 132 degrees, or 135? We’ll probably never know.

Thanks to the folks at NASA’s Earth Observatory for making these images available.