What are the reasons for the mass death of lemmings after the outbreak of their numbers?

Lemmings are animals that belong to hamsters. They mainly feed on plant foods. In “fruitful” years, their number increases sharply, since they have good conditions for this. But then there is not enough food for them. Lemmings start looking for their own food. They can even begin to eat inedible and poisonous plants. In search of food, they die. They often try to swim across rivers or bodies of water and drown. It was believed that they were committing suicide. But their death is associated with a lack of food.