Can a high load cause a system to reboot?

Not enough detail here...

But maybe, maybe not... This depends on the nature of the load and what's producing it. A high load on its own will not cause a system to reboot, but may be indicative of some other major issue that could cause an unplanned shutdown. E.g. a high-transaction mailserver or database server running a load of 80 is far different than a system whose RAID controller locks-up.

The easiest example could be storage. An instant rise in load following the loss of storage connectivity or a RAID controller malfunction could easily push the system load to 100+ on a busy system. The system may remain pingable and usable to some extent, but I/O operations could fail. Certain commands may stop working even though the TCP/IP stack is in memory and available.

So it's possible to kernel panic in this condition, or for the system or applications to stall. On quality hardware, there may be a watchdog timer that warm-boots the server. HP and the Automatic Server Recovery (ASR) feature or VMware's HA virtual machine monitoring could take this action.

It certainly could, but automatic reboot is usually associated with hardware/software issues such as overheating or kernel bugs. So it is possible that heavy load causes overheat which leads to reboot. In any event, you should investigate the log or kernel dumps to find the exact cause.

I think the answer is that no, high load on its own will NOT cause a system reboot. It will be a hardware issue or software issue of some description. Even if it always fails under high load it will be the high load triggering some other issue. I know this isn't much of a help but it does answer the question I guess :-)