Thermal imaging and rock slabs deformation due to daily solar radiation

<p>In the Yosemite National Park, it has been shown that large granitic exfoliation sheets can be subject to spectacular daily deformations (with cracks opening and closing with a magnitude of up to 15 mm over 24 hours). These thermal deformations, observed during hot summer days, are known to contribute greatly to rock falls. However, it is questionable whether this kind of deformation only occurs with exfoliation flakes (which have very particular shapes), or if it can be observed on more common rock faces geometries.  Moreover, does this phenomenon only occur during hot summer days or also in other seasons?</p><p>To answer these questions, cracks and slabs in two sedimentary rock walls were monitored over 24-hour cycles, in summer and winter. The first site is in the massive limestones of the old quarry of St-Triphon (in the Swiss Prealps), the second one in the cliff of la Cornalle (near Lausanne), an intercalation of poorly consolidated sandstone and marls. Air and contact temperature loggers, a pyranometer to measure the incident solar radiation and crackmeters were used in situ. Thermal images were acquired every 20 minutes (surface thermocouples sensors and aluminum reflectors are used to constrain the surface emissivity and the environmental radiative temperature).</p><p>First it was shown, that during sunny days, the amplitude of the daily variation of the rock surface temperature is as large in winter than in summer (up to 30°C). As expected, this amplitude is larger in the detached slab than in the massive rock mass. In both sites, the deformation measured in the cracks reach about 0.2 mm. Depending on the slab geometry and its “attachment points” with the main rock mass, an increase of temperature can correspond to a closing or to an opening of the cracks. In conclusions, however these daily deformations are about two orders of magnitude smaller than those measured in the Yosemite big walls, they appear to occur also in “common” rock faces all around the year. On the long term, these deformations will contribute to the rock weakening at sub-surface conditions.</p>

Demonic Mines

This chapter shifts attention from the hillsides to the shafts and galleries that miners hollow out underground. Via a close reading of Agricola’s De animantibus subterraneis (On Subterranean Creatures) and of sections of De re metallica not discussed in the previous chapter, as well as works by French writer François Garrault and by Paracelsus, this chapter asks if it is possible to understand “belief” in mining spirits as colluding with the chemical realities and medical dangers for humans connected with extracting matter. From this section, it thus emerges that for early modern humanists extraction of matter ex terrawas never just a question of human agents yielding extractive and controlling mastery over inanimate hillsides and underground rock faces.

A distinctive new species of Thelocactus (Cactaceae) from Oaxaca, Mexico

Thelocactus tepelmemensis, a distinctive new species of Cactaceae from northern Oaxaca, Mexico, is described and illustrated. The new species is closest to T. leucacanthus but differs significantly from this and other species in the genus by a combination of morphological characters: smaller, red-purple flowers; stems with ribs consistently vertical; lower number of spines per areole, these being usually shorter; ovoid fruit; and seeds with conjunct micropyle. The new species is found in a narrow canyon growing on steep limestone rock faces protected from direct afternoon sun. The only known population appears to be locally common but geographically restricted.

Mapping chromite deposits with audio magnetotellurics in the Luobusa ophiolite of southern Tibet

The exploration of podiform chromites in the Indus Yarlong Zangbo suture zone of southern Tibet has proved difficult because most known deposits pinch out and then reappear in the same direction. Several ground-based geophysical approaches such as gravity, magnetic, and controlled-source audio-frequency magnetotelluric (CSAMT) methods have been applied to explore for these chromite deposits but have mostly failed to delineate prospective areas. We have evaluated a successful podiform chromite exploration case history that is based on AMT. More than 8000 AMT stations were used in this study within a [Formula: see text] area of the ophiolite belt. Line separations were 80 or 40 m, and the station separation was 20 m. We implemented Bostick conversion and nonlinear conjugate gradient inversions for data interpretation, whereas 2D resistivity sections and 3D resistivity imaging were used to elucidate the inner structure and distribution of rock faces within the Luobusa ophiolite. Results from rock physics and drilling further indicate that resistivity-anomaly domains from these AMT results are correlated with rock faces in terms of fresh harzburgite, altered harzburgite and dunite, and they can thus be connected to concealed deposits. Therefore, we have developed three resistivity-anomaly models for chromite exploration, and we delineated several prospective regions containing exploitable deposits within the Luobusa ophiolite. Seven of the nine verified boreholes discussed in this paper intersected with chromite deposits; one comprises the largest and highest grade chromite deposit in China to date. Our AMT results provide the impetus for future chromite exploration in Tibet and enable a refined understanding of the structure and distribution of rock faces within the Luobusa ophiolite.

Animate Shadows of Bears and Giants

This chapter explores the performance of light and shadows in two ancestral Pueblo rock art sites in southeast Utah. These sites possess anthropomorphic rock faces and modified features to create both anthropomorphic and zoomorphic images that we argue derive from mythological traditions of Pueblo peoples. Specifically, light/shadow patterns at these sites produce and interact with Bear and War Twin imagery on prominent dates of the solar calendar. Traditionally such imagery would be approached through rock art studies in terms of motifs and symbolic interpretations. The celestial component would be addressed by archaeoastronomers. Using object agency theory, we seek to contextualize these data as places where people communicated with their Bear and War Twin deities.

THE POTENTIAL OF LOW-COST RPAS FOR MULTI-VIEW RECONSTRUCTION OF SUB-VERTICAL ROCK FACES

The current work investigates the potential of two low-cost off-the-shelf quadcopters for multi-view reconstruction of sub-vertical rock faces. The two platforms used are a DJI Phantom 1 equipped with a Gopro Hero 3+ Black and a DJI Phantom 3 Professional with integrated camera. The study area is a small sub-vertical rock face. Several flights were performed with both cameras set in time-lapse mode. Hence, images were taken automatically but the flights were performed manually as the investigated rock face is very irregular which required manual adjustment of the yaw and roll for optimal coverage. The digital images were processed with commercial SfM software packages. Several processing settings were investigated in order to find out the one providing the most accurate 3D reconstruction of the rock face. To this aim, all 3D models produced with both platforms are compared to a point cloud obtained with a terrestrial laser scanner. Firstly, the difference between the use of coded ground control targets and the use of natural features was studied. Coded targets generally provide the best accuracy, but they need to be placed on the surface, which is not always possible, as sub-vertical rock faces are not easily accessible. Nevertheless, natural features can provide a good alternative if wisely chosen as shown in this work. Secondly, the influence of using fixed interior orientation parameters or self-calibration was investigated. The results show that, in the case of the used sensors and camera networks, self-calibration provides better results. To support such empirical finding, a numerical investigation using a Monte Carlo simulation was performed.