A brief explanation of Ley Lines
The earth is striped by areas typically associated with mystical or unexplainable activity, or simply unexplained ancient structures. Places such as the Bermuda Triangle off Florida (US) and Stonehenge in England.
In times before the Rifts, these were places of mystery and superstition, but at the end of the Golden Age of man, the ample amounts of PPE free in the world makes these mystical lines actual visible manifestations. Extremely potent Ley Lines are visible even during the day as a silent crackling blue electric storm following a straight line. The greatest Ley Lines can be 480 km long and 3 km wide.
A longer explanation of Ley Lines
Normally, ley lines are not visible, but the energy is so great on
Rifts Earth that the lines glow day and night. During the day, the light
blue glow of the ley lines is barely noticeable. Travelers from a distance
might see the blue haze of a line in the distance, especially on an
overcast day, but they are nearly invisible on a sunny day or when actually
on the line in the daylight. (Just like you can't see the smog when
you are actually in LA, but you can't miss it as you approach from an
airplane or riding along the coastal highway.) At night, the ley lines
shine like a lit up highway and can be seen for miles.
When a Rift opens up, it usually happens at a ley line nexus, so a single doesn't often have a Rift appear. The only exceptions are a Rift opening during a Ley Line Storm or other heavenly event when ley line energy peaks (solstice, equinox, eclipse, planetary alignment). The size of a Rift may vary from pinhole to as tall as a skyscraper. Most start as a thin line or ripple of energy that appears in the air and begins to grow vertically. Then it begins to ripple with more energy and the line splits into two, with both halves moving apart at the center as if someone were pulling them apart. The Rift opening is usually near or at ground level, but sometimes appears high up in the air. However, most "man-made" dimensional portals created by magic are typically 7-25 feet (2.1 to 7.6 m) tall and 4-12 feet (1.2 to 3.6 m) wide. Most Rifts don't stay open for more than a few minutes unless they are controlled by a higher power or part of an unusual dimensional phenomenon.
During the Great Cataclysm and Two Hundred Years Dark Age, Rifts commonly remained open for hours, days and weeks. Even on Rifts Earth today, there are at least a dozen Rifts that are permanently locked open. (Permanently opened Rifts in North America: St Louis Rift/Devil's Portal - Calgary Rift/Monster's Gate. The Detroit and Windsor ley lines had Rifts at their nexus points locked opened for decades during the early part of the Two Hundred Years Dark Age, but closed about 130 years BPA - Before the Post Apocalyptic calendar began. Today, Random Rift activity in which Rifts open to various demonic realms and alien worlds remains high, but they are not locked open and seldom remain open for more than an hour or two.
Random Rifts are shadows from the Age of Chaos and seem to open and close for no reason, and may open for a few minutes or several hours, or longer. Random Rifts that flare and open on their own, without human intervention, seem to have genuinely opened to other times and parallel Earths as well as alien worlds and realities. It is believed that the dinosaurs arrived from Random Rifts during the Dark Age.
Time Rifting. Travel forward or backwards in time is believed to be possible through Rifts, but with the exception of beings like the Temporal Raider (see Rifts® World Book 3: England) and possibly Alien Intelligences and certain gods, no mortal sorcerer has been known to have mastered time travel. There are tales of mages accidentally opening a portal to another place and time and managing to return, but never on a consistent basis. Opening a Rift in space and to a specific time by the most talented and experienced Shifters, Rifters or Ley Line Walkers is a success perhaps once in a thousand tries. Even recognized incidents involving Rifting through time are a matter of debate among practitioners of magic. Conjecture is whether the person actually traveled through time or visited a parallel dimension that resembled a past or future time period.
Ley Line Nexus
At places where ley lines meet, or cross, a ley line nexus is formed. These are the locations where naturally occurring Rifts occur. The massive amounts of mystic energy actually bridge time and space and can create gateways to other locations and dimensions.