A volcano, which is not active, but is still registering seismic activity When there is no more seismicity, the volcano is dormant, but still capable of erupting (see active, dormant, extinct)
causing no symptoms; "a quiescent tumor" being quiet or still or inactive not active or activated; "the quiescent level of centimeter wave-length solar radiation" marked by a state of tranquil repose; "the quiescent melancholy of the town