You know that feeling when you are sitting on the edge of the volcano, looking into the fiery hellscape beneath? Remember how it felt when pulses of heat would hit you in waves, filling you with that sense of nature's power along with an ashy fullness that singed your hair and made you cough? Your eyes would dry out instantly, then start watering from the invisible soot and sulfur pushing you back, demanding you retreat from its awe and power. As you sat there, taking in the dry heat and recognizing you sat just above instant death, remember how you felt both terrified yet somehow at peace with the greatest forces our planet could show you - like looking into the eye of the Earth itself?
Oh - you haven't been on the edge of a volcano's crater?
Now, what really might get in the way of writing such an experience is not actually having it, and that's where the magic of writing takes over. In all honesty, you don't need to have been there to write about it. The writer's responsibility is to use words to convey the feelings that need to be realized. If the writer wants the whole volcano's edge experience to be terrifying, then convey whatever details you know about volcanos in the most fearful manner possible. If it's excitement that the reader needs to feel, then make sure every description is filled with adrenalin and energy. There are a lot of ways to frame the scene, and they should be direct appeals to the feeling the writer wants to communicate.
Of course, it has become obvious that the least important thing in the scene is the actual experience of being there. Whatever the truth of it is, that's not the important part; the feeling is. Now, if your writing piece is about a vulcanologist (volcano scientist) doing their work, you might want to explore some of those details of the profession. However, most of the time you can get away with using your imagination.
It may sound like cheating to use your imagination rather than researching volcano craters, and you are more than welcome to check all the YouTube videos you can find and go as deep into the subject as you wish. However, most readers will enjoy an emotional adventure into the crater more than they will appreciate your research, so give them something to remember - even if it's not from personal experience.
And, to clarify, I don't think I've ever been within sight of an active volcano, much less in the crater. If my readers want it, I will go there, but only in my words.