Westland Tai Poutini covers an area of approximately 130,000 ha from the Tasman Sea to its eastern border that is shared with Mount Cook National Park along the main divide. Its landscape ranges from a tropical coastline up to glaciated mountaintops of the Southern Alps.
The mountains rise rapidly creating steep and forested hillsides which are later replaced with snow fields and ice sheets above the tree line. Mount Tasman is the park's highest mountain and reaches almost 3500 m. The mountains in Westland Tai Poutini consist of layers of metamorphic schist, quartzite and greywacke.
The park counts over 60 glaciers. The most famous are the Fox and the Franz Josef Glacier since both of them reach 200 m into the lowlands. These lower lands in the west are covered by a moderate rainforest along several lakes, wetlands and rivers created through melting ice. The region is also known for its naturally occurring hot pools, that form in places where groundwater is geothermally heated.
Ice collapses, rock avalanches and sudden ice floods escaping from glacier terminals may occur at any time of the year.