As you can probably tell from the images the Haleakala has many amazing geologic and diverse landforms. The main material that the park is made of is lava rock, or obsidian. Knowing this, the Haleakala is a shield volcano, it last erupted between 1480 and 1600 A.D. When lava has hit the coast in the past, it has been predicted that smoke and sizzling ash hit the cool pacific ocean creating the jagged rock formations along the coastline.
When the volcano last erupted, a huge part of the mountain was blown off creating a 7.5 mile wide crater in the volcano. More recently cinders, ash, volcanic bombs, and spatter were blown from the numerous vents in the crater forming multi-colored symmetrical cones as high as 600 feet.