Thermal weathering of granite spheroidal boulders in a dry‐temperate climate, Northern Dobrogea, Romania

Abstract

Weathering microforms associated with exfoliation were investigated on 40 granitic spheroidal boulders identified on Pricopan Ridge (Măcin Mountains) in order to establish a spatial distribution pattern. Continuous thermal monitoring allowed the frequency and intensity distribution assessment of short‐term temperature changes triggered by summer storms, of intense day–night amplitudes and frost cycles across a uniform rounded boulder. Rock strength estimated by Schmidt hammer tests differentiates a significantly weaker resistance on the southern face of the boulders (rebound values of 27 to 33) in comparison with the northern face (43–50). The lowest resistance of the north–south cross‐boulder profile corresponds to the southern gentle slopes (0°–45°) thus defining the most susceptible area to exfoliation and other weathering processes. It is argued that this low‐resistant sector fits well with the maximum frequency and intensity of thermal processes recorded on the low and mid slopes (0°–45°) of the boulders south side, with small differences from one process to another, whilst the sector of 20° to 30° south corresponds to the peak activity of all. In accordance, the overlay map of exfoliated surfaces places the high frequency area on a spherical cap developed similarly (between 5° north and 45° south). The smallest exfoliated surfaces normally appear around 30° south and are inferred to extend in time both to the boulder top and downslope. The correlations between the frequency/intensity maps of thermal processes and the frequency map of exfoliated surfaces point to a complementary action in the exfoliated surfaces development of the short‐term temperature changes and diurnal cooling and heating due to the directional insolation effect, as similarly inferred in the development of meridional cracks. Copyright © 2016 John Wiley & Sons, Ltd.

Thermal stress weathering and the spalling of Antarctic rocks

“…Thermal fatigue weathering is likely a key weathering process in hyperarid, cold‐desert environments where the action of liquid water does not overshadow its geomorphic impact [ Eppes et al ., ; Eppes et al ., ; Hall , ; McFadden et al ., ; Molaro et al ., ; Vasile and Vespremeanu‐Stroe , ; Viles et al ., ]. In this study, we use a combination of field measurements, laboratory analyses, and numerical modeling to test the potential efficacy of thermal fatigue weathering in the spalling of thin (~2 mm) alteration rinds observed on clasts of Ferrar Dolerite on Mullins Glacier, located in the upland McMurdo Dry Valleys.…”

Mechanical weathering and rock erosion by climate‐dependent subcritical cracking

“…Accumulation of weathering products presumably “primes” this outer shell for wholesale exfoliation and/or susceptibility to thermal stresses, as proposed by some work [ Lamp et al , ; Tratebas et al , ]. A large majority of all subaerially exposed rocks show evidence of this type of surface parallel fracturing and/or granular disintegration regardless of environment and/or stress loading process. For example, freezing, fire, salt hydration, and thermal cycling have all been demonstrated to induce exfoliation [e.g., Al‐Omari et al , ; Turkington and Paradise , ; Vasile and Vespremeanu‐Stroe , ], and such spallation occurs in subsurface rock weathering as well [ Fletcher and Brantley , ]. Similar surface fragmentation models have been explored and validated, for example, in the context of dissolution weathering rinds [ Hoke and Turcotte , ] or salt weathering [ Wells et al , ].…”

Lichens Bite the Dust – A Bioweathering Scenario in the Atacama Desert

“…The large diurnal temperature range, for example (e.g. Jung et al., 2019a ), causes thermal stress (insolation weathering) in the granitoid particles as differences in mineral expansion set up cause the polycrystalline rocks to crack preferentially at grain boundaries ( Vasile and Vespremeanu-Stroe, 2017 ) which offers a great ecological niche for microbes of any kind. However, the bioweathering processes on which this study focused were those mediated by lichens, cyanobacteria and fungi that support the deterioration of rocks from a microscope to the landscape perspective and from the rock to the fine substrate as depicted in a possible chronosequence in Figure 1 .…”