Legends of Krishn's Ascension

According to researchers, Krishn ascended on 18th February 3102 BC. The period after his disappearance marks the beginning of Kali Yug. It is said that Krishn had predicted that exactly seven days after the ascension of the Lord, the Golden city of Dwaarakaa will sink in the sea and indeed Dwaarakaa is said to have been submerged into the sea owing to torrential rain. There are quite a few reasons assigned to Krishn's leaving his spirit for the heaven. They are as follows:

Fulfillment of Krishn's Birth Objective
Krishn came on the Earth with the primary objective of reducing the growing power of the demons and relieving people from their cruelties. The secondary objective was fighting the historical battle in Kurukshetra in order to deliver justice to Paandav. Having accomplished His missions and establishing peace, it was time for Lord to end His life journey on Earth.

Curse of Gaandhaaree
Mahaabhaarat, the historical battle fought in Kurukshetra resulted in the death of all the hundred sons of King Dhritraashtra and Gaandhaaree. Krishn is said to have visited Gaandhaaree after the war to offer His condolence. In a fit of rage and sorrow, Gaandhaaree cursed Krishn that just as the Kaurav dynasty had ended fighting with each other, similarly the Yadu Vansh dynasty would also end fighting and killing each other. Gaandhaaree felt that Krishn didn't play a fair role in putting an end to the war. If He wanted He would have stopped the war, but He let it go. Krishn happily accepted the curse.

Curse of Vishwaamitra and Naarad
According to a folklore, Vishwaamitra and Naarad once visited the city of Dwaarakaa to meet Krishn. A few children of Krishn dressed up Saamb (Son of Krishn and Jaambvatee) as a pregnant woman and asked the visiting sages to foretell what kind of a child Saamb will bear. Feeling insulted, the sages cursed that Saamb will give birth to an iron rod which in turn will be instrumental in the fall of the Yadu Vansh Dynasty. The very next day, Saamb gave birth to an iron rod. Krishn's sons crushed it into powder and threw it in the sea. Some small piece remained, that also was thrown into the sea. However, the powder grew into long sea grass and that small piece came on the seashore. One day an arrow maker found it on the shore and made an arrowhead out of it. He sold it to a hunter. Krishn could foresee everything and as a last resort to save His Dynasty, prohibited liquor in the city of Dwaarakaa. Eventually, the Yaadav became drunk and killed each other, first with weapons and after with that sea grass. That grass converted into iron rods and killed each other. None of them survived. Krishn was shattered to see the Dynasty perish.

Durvaasaa's Kavach
Once Durvaaasaa Rishi came to see Krishn and Rukminee. As everybody knew that Durvaasaa was an angry Rishi, they both welcome and entertained him very carefully. Whatever he wanted and asked was presented to him. After having the food he expressed his desire to eat Kheer (Paayasam). Immediately the Kheer was presented to Durvaasaa Jee. The Kheer was hot. Surprisingly Durvaasaa Jee did not the kheer brought for him, and asked Krishn and Rukminee to smear it on their bodies. Both Krishn and Rukminee were surprised to hear this but they could not have disobey Rishi, so both smeared their bodies with that Kheer. Krishn did not smear His feet with that Kheer. When Krishn saw this, he got very angry and said to Krishn - "I came here to put a Kavach on your body so that your body should be as hard as Vajra in any battle, but since you have left your feet un-smeared with this Paayasam, your feet are left now without Kavach. Now you will die because of your feet only." Krishn said politely - "Hey Muni, I could have never touched your Prasaad with my feet whatever it might have happened." Durvaasaa Muni got very pleased to hear this reply, but was sad that Krishn's feet remained vulnerable to death. And Krishn died because of His feet only.
(read this story in full HERE)

Ascension of Krishn
Krishn was disillusioned with the fraternal killing among the Yadu Vansh people. He went to a forest near Somnaath in Bhalkaa Teerth to meditate. Jaraa, the hunter who bought the arrowhead from the arrow maker, mistook Krishn's feet to be a deer and shot Him with the arrow. Krishn's spirit left for Heaven. Krishn's ascension marks the beginning of the current debauched age, also known as Kali Yug. Vyaas then wrote the famous 'Bhaagvat Puraan' to save the heritage and miracles of Krishn. The story of Krishn has since been passed from generation to generation.

Death of Balaraam
On seeing the end of Yadu Vansh clan, Balaraam, Krishn's  sat under a tree and ended his life by breathing out life from his mouth in the form of a white serpent.