Generation of shock lamellae and melting in rocks by lightning‐induced shock waves and electrical heating

Abstract

The very rapid energy release from impact events, such as those resulting from lightning strikes or meteorites, can drive a variety of physical and chemical processes which alter rocks and result in the formation of natural glasses (i.e., fulgurites and tektites). Fulgurite is the vitrified soil, sand, or rock resulting from lightning strikes. A thunderbolt is associated with air temperatures of up to 105 K, which can heat rocks to >2000 K within tens of microseconds. The rapid fusing and subsequent quenching of the surface of the rock leaves a distinctive, thin, garbled coating composed of a glassy to fine‐grained porous material. Previous studies on rock fulgurites found planar deformation features in quartz crystals within the target rock substrate, evidence of strong shock waves during fulgurite formation. In this paper, we simulated the shock pressure and temperature caused by an idealized lightning impact on rocks and compared the model results with observations on rock fulgurites from the literature. Our model results indicate that a lightning strike can cause >7 GPa pressure on the rock surface, generate a layer of fulgurite (of radius ∼9 cm), and leave a burned region (of radius ∼11 cm). The fulgurites found on rock surfaces share many features with sand fulgurites, but their spatial distribution is completely different, as sand fulgurites are hollow tube structures. Our study on rock fulgurites provides an indirect constraint on the energy of a lightning event and also demonstrates that the presence of shock features in rocks cannot be taken as unequivocal evidence for impact events.

Simulating electropulse fracture of granitic rock

“…As a result, high voltage pulses have also been used for drilling and mining applications [4,5,6,7,8], and in civil engineering demolition and recycling operations [9,3,10]. The e↵ect of high voltages on rock is also of interest in the study of fulgurites -rock formations produced as a result of lightning strikes [11].…”

Reply 2 to Comment on “Ultra-high pressure and ultra-reduced minerals in ophiolites may form by lightning strikes”

“…The thermal pulse apparently induced a shockwave sufficient to amorphise the K-feldspar lattice. For comparable lamellae in quartz in a fulgurite in a granite, Chen et al (2017) derived a minimum pressure of 7 GPa, well within coesite stability.…”

Earthquake and Electrochemistry: Unraveling the Unpredictable

“…Sample collected from PSZ [Taiwan Chelungpu-fault Drilling Project (TCDP)] shows features relating to melting or amorphous materials under SEM and TEM observations (25), which could be a signature of lightning-like discharge. Similar amorphous rock fulgurites (44,45) are formed due to lightning strikes on the quartz-rich soil/mountain. Okazaki et al (46) studied lawsonite dehydration as an earthquake triggering source in subducting oceanic crust.…”