The West Maui Mountains, West Maui Volcano, or Mauna Kahālāwai are the remnants of an eroded shield volcano that constitutes the western quarter of Maui. Approximately 1.7 million years old, the volcano's last eruption was approximately 320,000 years ago. Thanks to hundreds of inches of rainfall annually the mountains have undergone substantial …The West Maui Mountains, West Maui Volcano, or Mauna Kahālāwai are the remnants of an eroded shield volcano that constitutes the western quarter of Maui. Approximately 1.7 million years old, the volcano's last eruption was approximately 320,000 years ago. Thanks to hundreds of inches of rainfall annually the mountains have undergone substantial stream erosion. The ʻĪao Valley, and its Iao Needle are popular attractions within the mountains and are accessible from Wailuku.