Southernmost Africa, with extensive upland geomorphic surfaces, deep canyons, and numerous faults, has long interested geoscientists. A paucity of dates and low rates of background seismicity make it challenging to quantify the pace of landscape change and determine the likelihood and timing of fault movement that could raise and lower parts of the landscape and create associated geohazards. To infer regional rates of denudation, we measured 10Be in river sediment samples and found that south-central South Africa is eroding ~5 m m.y.−1, a slow erosion rate consistent with those measured in other non-tectonically active areas, including much of southern Africa. To estimate the rate at which extensive, fossil, upland, silcrete-mantled pediment surfaces erode, we measured 10Be and 26Al in exposed quartzite samples. Undeformed upland surfaces are little changed since the Pliocene; some have minimum exposure ages exceeding 2.5 m.y. (median, 1.3 m.y.) and maximum erosion rates of We directly dated a recent displacement event on the only recognized Quaternary-active fault in South Africa, a fault that displaces both silcrete and the underlying quartzite. The concentrations of 10Be in exposed fault scarp samples are consistent with a 1.5 m displacement occurring ca. 25 ka. Samples from this offset upland surface have lower minimum limiting exposure ages and higher maximum erosion rates than those from undeformed pediment surfaces, consistent with Pleistocene earthquakes and deformation reducing overall landscape stability proximal to the fault zone. Rates of landscape change on the extensive, stable, silcretized, upland pediment surfaces are an order of magnitude lower than basin-average erosion rates. As isostatic response to regional denudation uplifts the entire landscape at several meters per million years, valleys deepen, isolating stable upland surfaces and creating the spectacular relief for which the region is known.

Hydraulic engineering is increasingly relied upon to provide the necessary dry-season discharge for Peru’s hydroelectricity generation. Redirecting stream flow can yield unintended consequences, however, and here we document the wholesale contamination of the Lake Junin National Reserve by acid mine drainage from the Cerro de Pasco mining district. Since construction of the Upamayo Dam in 1932, the Rio (river) San Juan, which drains the Cerro de Pasco region, has been seasonally redirected into Lake Junin. As a result, the upper several decimeters of sediment in the lake contain peak concentrations of Cu, Zn, and Pb of ~6000 ppm, ~50,000 ppm, and ~2000 ppm, respectively, with the latter two greatly exceeding the United States Environmental Protection Agency (EPA) limits for the entire 150 km lake basin. That the source of the contamination to Lake Junin is acid mine drainage from Cerro de Pasco is supported by spatial gradients in metal concentrations, authigenic calcite (marl) concentrations, and the isotopic record of Junin water. Today, the upper 50 cm of sediment in Lake Junin contain ~60,400, 897,600, and 40,900 metric tons of Cu, Zn, and Pb, respectively, which is equivalent to ~5.1 years’ worth of Zn extraction and ~0.7 years’ worth of Pb extraction from mining operations at Cerro de Pasco at current rates.

The Paleozoic Variscan orogeny was a large-scale collisional event that involved amalgamation of multiple continents and micro-continents. Available structural, geological, geochemical, and geophysical data from Iberia are consistent with a model of oroclinal bending at the lithospheric scale of an originally near-linear convergent margin during the last stages of Variscan deformation in the late Paleozoic. Closure of the Rheic Ocean resulted in E-W shortening (in present-day coordinates) in the Carboniferous, producing a near linear N-S–trending, east-verging orogenic belt. Subsequent N-S shortening near the Carboniferous-Permian boundary resulted in oroclinal bending, highlighted by the formation of the Cantabrian Orocline. Together, these data constrain oroclinal bending in Iberia to have occurred during the latest Carboniferous over about a 10-million-year time window, which agrees well with recent geodynamical models and structural data that relate oroclinal bending with lithospheric delamination in the Variscan. This late-stage orogenic event remains an enigmatic part of final Pangaea amalgamation.