The Himalayas were formed as a result of the collision between the Indian Plate and the Eurasian Plate. This event began around 50 million years ago and continues to this day. This is not due to a mid-ocean ridge splitting apart, a transform boundary shift, or an increase in volcanic activity, but rather a convergent boundary where two continental plates collide.
As the Indian Plate moved northward from the south, it collided with the much older and larger Eurasian Plate. This collision caused the sedimentary rocks that lay in between to be compressed and pushed upwards, leading to the uplift of the Himalayan mountain range. This process is known as orogeny, specifically continental collision or orogenic uplift.
Additionally, the Himalayas are also influenced by ongoing tectonic processes, including earthquakes resulting from the continuing movement of these plates. The intense pressure and stresses from the collision have led to the formation of not just mountains but also deep valleys and high plateaus characteristic of the region today.
In summary, the formation of the Himalayas is primarily a result of tectonic plate collision, not a mid-ocean ridge, transform boundary, or volcanic activity.