I'm planning to compete in a 75km race with 4 1000 meter vertical assents in October. This is about as mountainous as you can get in Australia. This is a walk in the part compared to the races in Europe, New Zealand and North America, which have more geologically recent mountain ranges, and communities in which alpine / mountaineering / orienteering and running cross over.
I've heard Anton Krupicka (well known and achieve North American ultra racer) refer to the UTMB (the most well known ultra marathon race in Europe, in which a loop of Mt Blanc taking in 3 countries is done) as "unexpectedly flat"
I look at the course profile for that, and the course profile for the 4 1000m assents for the 75km race I'm doing in October and think "how do that many people finish".
The US has harder races, which still have remarkably high finishing rates. The "Hard Rock 100" (miles) is basically at times a rope-free scramble up mountain tops, and it has a remarkably high finishing rate (when we're talking more that 10% of the field finishing, it's remarkable)
It's quite amazing the variation among ultra races, and 100 miles is not just 100 miles.
The interesting thing is that many of the trail / mountain runners need that sort of variation for psychological reasons and find things like 100 mile tarmac races to be more psychologically and physically taxing. A mountain / trail race having highs and lows geologically, mentally, physically but a flat tarmac race having less variation being harder to switch out of a down patch, and requiring serious inner resilience to counter-act a "runners low".
Good luck! Just remember: don't decide to quit while going uphill.
Hardrock has a high finishing rate because each of the 140 starters has already completed a difficult 100 mile race and likely years of lottery attempts to get in (Krupicka finally got in this year). Most other 100 mile races in the States are easier to enter and so have a smaller finishing rate.
But while a healthy reasonably-trained adult has a solid chance of completing Hardrock simply by putting one foot in front of the other and not giving up, Barkley apparently needs something more. Of the three people I know who started, including one this year, none finished. If physical ability and tenacity were enough all three would have finished. It's that hard.
I'd disagree on your assessment that a reasonably-trained adult can finish hardrock. I've done it twice. It's an almost full-time commitment to get in the training, and also you have to get out there a month in advance just to acclimate. I've done a lot of those type of races, and hardrock is the hardest.
I'm surprised there's nothing more extreme in Australia. I'm in Adelaide, and we have road cycling events with 4000m climbing in 140km. You don't need high mountains to get the total elevation, just lots of steep climbs.
We generally don't have sustained climbs, especially like those in Europe. In cycling terms, we don't have an Alp d'Huez or a Tormalet - something that is 15+ km of HC climb.
We tend to either 2 - 5km of sharp steep stuff, or maybe up to 15km of less sharp (like cat 3/4) climbs.
It's that sustained climbing at > 9% that will get ya.
You don't need the high mountains to get lots of total climbing. Look at the Ardennes races coming up in Belgium, or even the Amstel Gold race - 4000 meters of climbing in the Netherlands!
"I'm surprised there's nothing more extreme in Australia. I'm in Adelaide, and we have road cycling events with 4000m climbing in 140km."
There is.
"completed the gruelling challenge in 37 days, 20 hours and 45 minutes, pedalling more than 377 kilometres a day ... On one occasion I rode right through the whole 24 hours and we got through 506 kilometres, "
Sorry, I should make it clearer. I used the word extreme to designate hilly. In the context of the original poster it's pretty clear:
From the OP: I'm planning to compete in a 75km race with 4 1000 meter vertical assents in October. This is about as mountainous as you can get in Australia. This is a walk in the part compared to the races in Europe, New Zealand and North America.... I look at the course profile for that, and the course profile for the 4 1000m assents for the 75km race I'm doing in October
The whole point is that you don't need high altitude to get extreme elevation change in a race. I'm more familiar with cycling, but in that sport there are probably only about 4 or 5 rides in the world we can't match in terms of hill climbing, and those are either extremely long continuous climbs (eg, Haleakala, Alto de Letras; our longest is 30km) or 10km+ at extreme gradients (over 10%; Mount Zoncolan, Alto de L'Angliru; out longest is around 9km).
Generally you can make the race harder by looping it over steep terrain, just like the Barkley does.
I was hoping the OP could enlighten me as to why we don't have trail runs in Australia that are just as challenging.
Hardrock has a high finisher rate because of the exhausting lottery system. You have to run a specific mountain 100 mile race in preparation. Also, Most of those people are returning runners.
I've heard Anton Krupicka (well known and achieve North American ultra racer) refer to the UTMB (the most well known ultra marathon race in Europe, in which a loop of Mt Blanc taking in 3 countries is done) as "unexpectedly flat"
Here's some footage of that race: https://www.youtube.com/watch?v=St49BdhuA8c
I look at the course profile for that, and the course profile for the 4 1000m assents for the 75km race I'm doing in October and think "how do that many people finish".
The US has harder races, which still have remarkably high finishing rates. The "Hard Rock 100" (miles) is basically at times a rope-free scramble up mountain tops, and it has a remarkably high finishing rate (when we're talking more that 10% of the field finishing, it's remarkable)
It's quite amazing the variation among ultra races, and 100 miles is not just 100 miles.
The interesting thing is that many of the trail / mountain runners need that sort of variation for psychological reasons and find things like 100 mile tarmac races to be more psychologically and physically taxing. A mountain / trail race having highs and lows geologically, mentally, physically but a flat tarmac race having less variation being harder to switch out of a down patch, and requiring serious inner resilience to counter-act a "runners low".