In 2010, between April, 15 and April, 23, Air Travel was disrupted because of the ash cloud generated by the icelandic Eyjafjallajökull eruption.
That meant a lot of travellers could not reach the beds they had booked, while approximately the same number of people could not leave their beds to return home. On the first day, the volume of calls making it into the call center (not counting dropped calls) was nine times the normal volume. We added a lot of personal (three times the normal staff, IIRC) to call centers, upgraded servers to handle the increased churn on the databases, and added licenses to the phone system to cope – all in all an extremely busy time.
Also, many hoteliers realized that it is actually ok for customers to cancel, as long as the beds are warm (and paid for). Travelling became a lot more flexible in the aftermath of this incident.