The Mt St Helens climb is actually, for the most part, hiking, except stepping and climbing the boulders. These are the distinct parts of the route: The forest trail up to the tree line, the boulders, and the last, steepest and hardest part: hiking in sand and ash.
Plan ahead, start early
You have to be at least in a decent shape in order to climb. It will be a tough hike, but you can make it. If you are not in top shape, head out early, 6:00 am, or even earlier. That should give you enough time to be back before dark. I am in little better than average shape and can make it in less than 8 hours. People in top shape can do the round trip in 5 hours or less. The distance from the trail-head to the top is 5 miles. First 2 miles in the forest, 3 miles from the tree line to the crater rim. And then the same way back.
The 3 miles from the tree line to the crater rim are the hardest, and takes the longest time. The terrain becomes more rugged, and much steeper. The air gets thinner as you gain elevation.
From the parking lot to the tree-line
Make sure you are dressed properly for the hike, and that you have everything you need with you. Put some sunscreen on! Take it easy on the forest trail, and save your energy for the steeper parts. There is a bathroom toward the end of the forest trail for a last rest-room stop before the climb.
From the tree-line to the crater rim
Once you are out of the woods, and out on the rocks and boulders, there is hardly any visible trail rest of the way up. Now you need to rely on vertical route marker poles placed along the route. At each post, you are able to see the next post on the route. You don’t have to trek straight from post to post, but rather, look for easy passage, always keeping the posts in sight.
The climb is best done at a slow and steady pace, with only quick breaks, if needed. If you stop too long, your body start cooling down and your muscles start to stiffen, and you don’t feel as energized to keep going. Keep yourself hydrated, and keep energy snacks handy.
At steeper parts, especially in the boulders, instead of hiking straight up, it might be easier to ascend in a zig-zag pattern. It makes the hike longer, but not as steep.
Generally, it is best to stay on the ridges, but you can also hike on the sides of the ridges. Going back and forth between ridges and the lower areas is a waste of time and energy (unless you have plenty of both). Depending on how much snow there is, you can also hike on the snow. Be careful though if you are walking on the glacier, watch out for crevasses. The big cracks can be covered by snow at the surface, and if you fall through into a deep crack, you might not be able to get out. For this reason, it is safer to walk closer to the edge of the glacier, Also, walking on the glacier, you need to be careful that you don’t loose your balance. It would be better to wear cramp-ons. I prefer to walk on the rocks, it seems to be easier and more fun.
Reaching the summit
Once you reach the top, get some warmer clothing on, take a break, and enjoy the views. This is the favorite spot for most people to have their lunch break.
Don’t get too close to the edge of the crater rim! There are markers showing how far on the rim it is safe to be. Even in the summer, there is an ash-covered snow overhang on the rim, and people have fallen down in the crater and died, when stepping on it and it has given way.
The hike down
The hike down is of course much easier, and will be much quicker. But it might still not be easy. You are already worn out, and still need to hike miles over rugged terrain. It might not be a good idea too jump on the boulders too much, since it is hard on your calves. I learned the hard way, jumping on the boulders too much on the way down, and suffering the last two miles through the woods with my legs badly hurting.
You can also do some glissading, sliding on the snow. Bring a piece of plastic to sit on. Keep the speed down. If you lose control of your speed, there is no stopping until you hit a rock at high speed. You can use a trekking pole as a break at very slow speeds, but only effective stop is using an ice axe. I prefer less steeper and shorter slopes for glissading, just to stay safe.
Watching the video below, you will get a good idea of what the hike is like.