Geological considerations of contemporary military tunnelling near Mosul, northern Iraq

Members of the so-called Islamic State (IS) have used subterranea in Syria and Iraq as a core part of their control over territories and their military capability. Around Mosul they exploited existing natural sinkholes, caves and tunnels. The use of tunnels and the completion of new ones between 2014 and 2017 impacted the advance of Iraqi and Peshmerga forces in the battle for Mosul. IS created complex tunnel networks using hand tools, power tools and improvised tunnel-boring machines. To avoid detection, tunnels were started in buildings and spoil was hidden in rooms. The tunnels range from those large enough for one person to crouch in to those large enough for a vehicle. The most sophisticated tunnel complexes had dormitories, hospitals, armouries, kitchens, latrines, and command centres complete with CCTV, solar panels, computers, phones, electricity, respirators and ventilation facilitating underground occupation for long periods. IS tunnelled in almost all urban areas they controlled, demonstrating an enormous effort: moving from hand tools to tunnel-boring machines was a logical progression. The size of tunnel-boring machines and the amount of spoil generated defined the type of building they started in and the length of the tunnel they bored. Buildings with tunnels under them risk collapse.