Alli is a tan pegasus with a lavender mane and tail, and lighter streaks through it. She typically keeps her hair well-brushed, but otherwise puts fairly little effort into styling it. Her cutie mark is an erupting volcano. For unknown reasons, she's shorter than most ponies, even for a pegasus, though she seldom seems to mind.
Her personality is friendly and playful, if a bit unimaginative at times, and while she's naturally shy, she tries to be outgoing in hopes of compensating for that. She enjoys occasional flying, but usually prefers life on the ground, and treats her flying abilities more like a casual hobby than a vital skill, unlike most pegasi.
Alli was born in a small frontier settlement on the edge of the Dragonlands border, about a full day's flight south of Ponyville. Her father was a cargo-pegacoach puller who taught her to fly during their re-supply trips to Cloudsdale, and her mother was a weather pony, who had to make her own clouds at home due to the harsh conditions. When Alli was a young filly, their settlement had to hastily evacuate due to a volcano eruption, and while the adult ponies around her were terrified, she was fascinated by the eruption. Awestruck by the incredible sight, she was overwhelmed by a desire to learn everything she possibly could about it, and while her parents were pulling her away to safety, her cutie mark formed.
Unfortunately, her parents were rather traumatized by the experience, and moved to the opposite side of Equestria, to Cirruston, to get as far away from volcanoes as possible. She was uncomfortable making friends her own age, and constantly terrified of the water below the city, so the second half of her childhood wasn't exactly fun for her. Eventually, she learned to enjoy the water, but she never quite adjusted to living in a large city.
Alli's cutie mark and career goals were always a point of tension with her parents, but they didn't stand in her way when she pursued a degree in Geology at the University of Trottingham. She studied hard, even taking extra classes in the science department, and her school performance was usually exemplary. With the number of rowdy stallions in the city, and the relatively small population of pegasi, Alli never quite felt welcome there.
For her senior project, she chose to do original research on the geological composition of the Everfree Forest, in hopes of unlocking some of its mystery, and in hopes of impressing the entrance committee at the University of Canterlot for graduate school. This decision led her to stay in Ponyville, a town she rapidly fell in love with, enchanted by the welcoming, supportive environment of the town. She even expressed a desire to relocate there permanently after graduation, but her educational career has taken her to other locations.
After she returned to the University of Trottingham to present her research, following her extended trip to Ponyville, she graduated with honors with a degree in geology. But, before she could submit her graduate school application to the University of Canterlot, she was approached by the Haywaii Geoscience Institute, who offered her a full scholarship toward a master's degree in seismology after reading her research report on the potential new fault system she discovered in the Everfree Forest. Since then, she's been working on a new method of seismic surveying to study the compositions of Haywaii's many volcanoes.
Her eventual career goal is to work for the Equestria Geological Survey, preferably as a volcanologist or seismologist.
In addition to her considerable knowledge of most areas of geoscience, and a particularly thorough knowledge of volcanology and tectonic theory, her early years on the mountainous frontier led to her developing strong survival skills. She also has a natural skill for taking care of foals, and often used to "foalsit" Tornado Bolt and his friends when she lived in Ponyville.