Here's why:

* Temperate glaciers are glaciers that are at or near the pressure melting point of ice. This means that the bottom layer of the glacier is at a temperature close to 0°C (32°F), regardless of the air temperature above.

* Vatnajökull is located in Iceland, a country with relatively warm temperatures for a glacial environment. The glacier's base is close to the pressure melting point, allowing for a significant amount of meltwater to flow underneath and within the glacier.

* In contrast, polar glaciers are much colder and frozen to the bedrock, meaning they don't have significant meltwater flow underneath.

While Vatnajökull is a temperate glacier, it's also the largest ice cap in Europe, with a vast area covered by ice. It's a complex glacier with varied characteristics, including both fast-flowing outlet glaciers and areas of slower moving ice.