The insolation of a porous body in a low-pressure environment results in a temperature gradient inside the body and leads to a sub-surface gas flow. This gas flow, called thermal creep, influences the in-depth pressure distribution. Hence, the pressure increase in the near-surface layer sets the surface material under tension, which will lead to erosion. To visualize the layer under tension and quantify its thickness we employed Diffusing Wave Spectroscopy, or short DWS, where the interference pattern of a laser illuminating a sample is analyzed. DWS is a technique utilizing the calculation of correlation maps between the speckle patterns, captured at different times, and this way allows studying the dynamics of small-scale motion within the sample. The correlation maps consist of smaller areas containing information about the deformation in the given area and are spatially resolved. So, this technique allows one to see the average nm-scale-movement of particles enclosed in a small volume (in our case around 0.008 mm<sup>3</sup>) on a sample. We used basalt powder with an average diameter of around 50 µm as a sample, which is contained in a squared glass vessel and is heated from above. The speckle pattern generated by the sample is recorded by a video camera. We investigated an area of around 2 cm<sup>2</sup> on the sample. In our study, we observed a minimum of movement at around 2 mm below the surface, which can be traced back to the pressure maximum in the vicinity of the minimum of motion. The deformation above, or below the maximum is pressure-dependent and is largest at an ambient pressure of around 3 mbar for our sample, which is in accordance with thermal creep as the source. This effect can dissolve planetesimals in the inner regions of protoplanetary disks as soon as they emerge into stellar light.