New main objective: Close the rupture
Note! The mission is optional and has random guidelines. I'd recommend repeating it from time to time, as you can enrich yourself and increase your fighting skills. You will get the chance to approach this quest no sooner than after finishing the last main quest of the College of Winterhold, Eye of Magnus.
Find Tolfdir (he's usually at the main square of the college or at the Hall of the Elements) and ask him if there's anything more he would like to talk about (screen above). As a result, the mage might (it's not certain) give you this quest, informing that a rupture has appeared in a random part of Skyrim and needs to be closed.
New main objective: Talk to Tolfdir
Open the world map and head to the marked location. After getting there, start attacking the Magic Anomalies known from previous quests (screen above). You can follow Tolfdir's suggestion and use the Staff of Magnus, though it's not necessary. If your character is good with weapons of knows powerful offensive spells, it would be even better to use only them. After eliminating all the Anomalies, return to Tolfdir. The mage will rewards you with gold, though only if the rupture was outside the College.