Electric power systems are threatened by the occurrence of natural disasters (such as volcanic eruptions, earthquakes, hurricanes, among others), which cause important damage to different elements of the system, thus significantly affecting its ability to supply energy. In this context, there is currently a strong demand for developing appropriate resilience assessment techniques to capture the impact of natural disasters and evaluate relevant mitigation strategies. This paper proposes a methodology to assess the impact of volcanic lahars on the electric power systems, using Monte Carlo simulations to determine the vulnerability of system elements. The proposal includes a DC optimal power flow model (DC-OPF) to represent the Economic Dispatch for operating the electric power system in the contingency scenarios generated, and quantifying the energy not supplied (ENS) of the system. The proposed methodology is applied in the IEEE 24-bus test system and Ecuadorian National Interconnected System (NIS) to obtain metrics and evaluate the resilience of the system. The results show that the methodology is able to quantify the degradation of resilience in terms of operation and infrastructure of the electric power systems against the occurrence of lahars.