Mannahatta Hotspot

Most people don’t know that an active volcano rumbles deep beneath the Manhattan Schist. Created during the Taconic orogeny 450 million years ago, the volcano still erupts periodically, filling subway tunnels with lava (hence the delay on the Second Avenue dig), and filling the sky with acrid smoke and ash, which many people attribute to apartment building incinerators and vehicle emissions. The City employs almost 7,000 engineers, technicians, and laborers to manage the risk. Pictured here is one of the Midtown steam vents. The orange cone sits atop a 9,300 foot vertical shaft drilled to release pressure from Mannahatta’s magma chamber. Before the City began sinking these vents in the 1960s, it was common for the street to rise as much as five feet above a hot spot. On rare occasions, too much pressure builds up, and the vent fills with lava, leading to street closures and evacuations.