 Complete the following phrase:  In 1970, a group of mountain climbers together with Heckel planned to visit Alaska. Their intention was thwarted by the Czechoslovak communist regime. Following the suppression of the Prague Spring in 1968, it was almost impossible to travel to Western countries. The group changed their plan and decided to climb the peaks in the Peruvian Cordillera Blanca. Heckel and several of his colleagues planned to leave the expedition and focus more on studying and documenting of Peruvian culture. However, after the death of one of the leaders of the expedition, climber Ivan Bortel, they were forced to stay in the camp with the rest of the expedition. On 1 June 1970, Heckel and his colleagues intended to separate from the rest of the group. Coincidentally, the avalanche caused by 