Eastern South Asia region is bounded by Nepal, Sikkim, and Bhutan in the north, Bangladesh in the east, the Indian states of Uttar Pradesh and Chhattisgarh on the west, and the Indian state of Andhra Pradesh in the south. It is connected to the Seven Sister States of Northeast India by the narrow Siliguri Corridor. West Bengal is on the eastern bottleneck of India, stretching from the Himalayas in the north, to the Bay of Bengal in the south. The region lies in the humid-subtropical zone. The landlocked region of Northeast India includes the states of Assam, Arunachal Pradesh, Bihar, Mizoram, Manipur, Meghalaya,
Himalayas current valley glaciers of the Himalaya reach at most in length, several of the main valley glaciers were long during the ice age. The glacier snowline (the altitude where accumulation and ablation of a glacier are balanced) was about lower than it is today. Thus, the climate was at least colder than it is today. Despite their scale, the Himalayas do not form a major watershed, and a number of rivers cut through the range, particularly in the eastern part of the range. As a result, the main ridge of the Himalayas is not clearly defined, and mountain passes are