Types of Climbing
The standard disclaimers about how dangerous climbing is and how unreliable anything is you read anywhere apply here as well. This site is far from definitive (and probably far from accurate). It is here for the amusement of myself and friends and possibly to shed some light, though I don't mind a little obfuscation now and again either. Various parts have been adapted and pilfered from sources found hither and yon, though I have tried to make all entries mostly original. So please read, but remember that responsibility for safe climbing is your own.
This is climbing on boulders or low rock walls (<15 feet) without ropes, but generally with a large crash mat beneath you and a set of friends to catch you. Bouldering is about climbing on rock and practising the hardest moves possible, but in a very low (i.e. safe) environment, and without the necessity to manage gear and ropes. As a result bouldering is often about power, and boulderers tend to have the silliest muscles of the climbing fraternity.
It is also the part of climbing which corresponds most to skater kid culture. The rules are:
1. wear a beanie hat.
2. take off your top, to get maximum muscle exposure
3. go out with a load of your (and this is important, MALE) friends.
4. Hang around in a group at the bottom of the boulder, whilst each of you tries the problem in tun.
5. Whilst not climbing or spotting (i.e. ready to catch), talk loudly about cars, "chicks", how much you drunk last night and how hot the curry was.
6. If women are invited, they are to sit down looking pretty admiring your muscles.
OK, there's a fair amount of tongue in cheek about that, but not as much as you might think.
Boulder problems can get a bit scary, as there's quite a lot of "highball" problems (i.e. >15ft), where the crash mat and your mates might not save you getting a really bad injury.
It's also possible to land badly, of course, from any height (including a mate of mine who badly broke his ankle falling from 18 inches up onto a 9 inch thick crash mat).
Saying all of the above, however, bouldering with a group of friends can be good fun. You get to try really hard stuff, there's the whole "your mates egging you on" thing, you get to all try the problems in turn and learn from each other, and its basically a way of climbing at and beyond your (technical and physical) limit without being in much danger.
Climbing full size routes without ropes. What is defined as "full size" is a matter for opinion and, often, heated religious debate ("that's not high enough to be a route, its only 6m, that's a boulder problem, etc, etc.") Even those wishing to start arguments tend to shy away from comments like
"Is "The Curse" at Burbage North a boulder problem or a route?"
as its so hard to get the blood out of the carpet afterwards.
Soloing is dangerous. There is no safety system, so if you fall off you are seriously injured or dead. Given on any route there might be loose rock, or a hold might break off as you put your foot on it, there might be loose gravel, etc, you are dicing with your life. As a result most soloists solo much easier stuff than they are actually capable of at their best with a full roped system. What is defined as "easy", of course, depends on the person.
Saying that, however, its the most enjoyable form of climbing, in my opinion. Nothing to worry about apart from you and the rock. No harness, no ropes, no gear. You get a wonderful "at one with the rock" feeling, and are free to move across the rock at will. Just don't fall off, eh?
Ignoring where the belay actually is (there's another debate about whether "top-roping" should actually be called "bottom-roping") you basically have a rope which goes from your harness to the top of the route. As you climb up, that rope is taken in by your belayer, so you are always tight(ish) on the rope. As a result, on a vertical route (as opposed to a traverse), if you fall off then, with an alert belayer, your "fall" should be a matter of inches before the rope is tight. The safest form of climbing outside.
4. Leading and seconding.
The normal way of doing it. The leader climbs the route with a rope attached to his harness. As the leader climbs the belayer lets rope out. As the leader passes the protection points he clips the rope in. This, in theory, means that any fall is limited to double the distance between the leader and the last bit of protection.
The Leader then gets to the top of the route and sets up a secure belay, and pulls the rope through to the point where the belayer can tie into the end of the rope. The belayer (now "seconder") climbs the route removing the protection until he reaches the leader.
Why two ropes?
There's several reasons.
Two ropes are safer than one. It is possible for a rope to be cut in a rockfall, it is possible for a rope to be cut if a climber falls on it and it is loaded over a sharp edge. Two ropes pretty much eliminates this.
2. Rope drag
On a traditional route the route may wander all over the place. Also, the leader may place protection alternately right and left of the climb. If using one rope the drag from the rope passing through sharp bends will result in significant rope drag, and clipping one rope right and the other left means, with good ropework, that rope drag is significantly reduced.
3. You can abseil twice the length of the rope
4. If you have to abandon one rope, you can.
I have had the situation where, when climbing, one rope has been caught in a crack, and got itself securely jammed, so preventing the climber from continuing. With two ropes you can (and I did) untie from one rope and continue on the other.
Climbing on two ropes, which are both clipped into every piece of protection. The main reason I've seen this done is in icy weather, where the figure-of-eight shaped cross-section is easier for the belayer to grip, when both their hands and the rope are icy.
This used to be very common, and still is in some places in the world. Basically steel pegs are driven into cracks and other natural breaks in the rock rather than normal nuts and cams. Don't try it in the UK unless you want to get lynched.
6. Via ferrata
Used a lot on the continent. Basically a system of ladders and wires bolted to the rock which you can clip into. It alows you to move very fast across steep terrain.