Field Observations on Lava Deposits from the May 22nd, 2022, Eruption of Mt Nyiragongo, DRC

High velocity lava flows from Nyiragongo volcano pose a severe threat to Goma town and surrounding villages, as documented by the 1977, 2002 and, most recently the May 2021 eruptions. During the eruption on May 22nd, 2021, lava flows erupted from four distinct fissures: Shaheru, Kaneza, Mujoga and Lemera-Makao. The eruptive fissures are related to tectonic activity in the western branch of the East African Rift and are oriented NNW-SSE. They follow the same orientation as those from the 2002 and 1977 eruptions. The eruption itself was short lived and lasted only about 8 hours. It was characterized by lava fountaining from the fractures, which fed two lava fields of both channelized and sheet flow systems.

Here we present an updated map of the eruptive deposits formed during the eruption on May 22nd, 2021, as well as detailed field observations and measurements of lava flow features that were taken during two field campaigns in 2021 and 2022. We document changes in the surface morphology along and across the 2021 lava flows, that commonly start as Pāhoehoe surfaces and transition from these smoother surfaces to ʻAʻā surfaces at varying distances; 2.5Km (Kaneza fissure), 3.5Km (Mujoga fissure), 7Km (Shaheru fissure) and 1Km (Lemera-Makao fissure). These along-flow transitions in surface morphology suggest that the lava underwent significant, syn-depositional changes in rheology. Further, we map the transitions from channelized to sheet flows and present measurements of lava flow channel widths, depths, and height, as well as the width of spatter aprons uphill of the four eruptive fissures. These measurements are used to estimate lava fountain heights in the absence of syn-eruptive measurements.