Wiktionary
impassability
n. The state or quality of being impassable.
Usage examples of "impassability".
Travellers keep coming in with stories of the impassability of the roads and the carrying away of bridges.
On the descent, when things began to look very bad, and the mountain-sides had become cascades bringing trees, logs, and rocks down with them, we were fortunate enough to meet with two packhorses whose leaders were ignorant of the impassability of the road to Odate, and they and my coolies exchanged loads.