What is ben nevis made out of?

Answer 1

Igneous rock. this is a hard rock, which explains why it is still left standing, it is less susceptible to erosion. the lake it surrounds is made of sedimentary rock, which is softer so it eroded away.

Answer 2

"Ben Nevis consists mainly of igneous rock from the Devonian period (around 400 million years ago), intruded into the surrounding metamorphic schists; the intrusions take the form of a series of concentric ring dikes. The innermost of these, known as the Inner Granite, constitutes the southern bulk of the mountain above Lochan Meall an t-Suidhe, and also the neighbouring ridge of Càrn Mòr Dearg; Meall an t-Suidhe forms part of the Outer Granite, which is redder in colour. The summit dome itself, together with the steep northern cliffs, are composed of andesite and basaltic lavas. The mountain has been extensively shaped by glaciation."