clastmelt

Clastmelt refers to a geological process where solid rock fragments, or clasts, are partially or completely melted due to extreme heat, typically within a volcanic environment. This phenomenon commonly occurs during explosive volcanic eruptions, particularly in pyroclastic flows or surges, where high temperatures and pressure cause fragmentation and partial melting of existing rock. The term is often used in the study of volcaniclastic deposits, which are sediments composed of volcanic fragments.

During clastmelt, the heat source is usually magma or lava, which can reach temperatures exceeding 700–1,200 degrees Celsius (1,300–2,200 degrees Fahrenheit). When magma interacts with cooler, solid rock, the outer layers of the clasts may soften or melt, creating a glassy or partially crystalline matrix that binds the fragments together. This process can produce distinctive volcaniclastic textures, such as welded tuff, where clasts are fused by melted material.

Clastmelt is significant in understanding volcanic processes, as it helps geologists interpret the intensity of eruptions and the thermal history of volcanic deposits. It also plays a role in the formation of certain igneous rocks, particularly those found in volcaniclastic sequences. By studying clastmelt features, researchers can infer conditions like eruption temperature, magma composition, and the presence of hydrothermal activity.

This process is distinct from other melting mechanisms, such as regional metamorphism or partial melting of mantle material, as it occurs rapidly and locally within volcanic systems. Clastmelt is particularly well-documented in pyroclastic rocks from stratovolcanoes and calderas, where explosive interactions between magma and country rock are common. Its study contributes to broader fields like volcanology, petrology, and sedimentology.