In the alphabet Hagalaz corresponds to the letter "H". It is known by the names Hagalz, Haegl, Hagal - Hail and Snow. It has been equated with the deity Hella, but I believe it has more of an association with the "Norns", as it is destruction that leads to "change". Hagalaz has an assimilation with the Yew and Ash trees. It's color is light blue and it corresponds to the "The World" card in the Tarot. Astrologically it would be "Aquarius."
In the first aett, set of runes,they dealt with emergence of order out of chaos. Hagalaz is the first rune of the "second" aett. It creates disruption and disorder, but it also brings about necessary change and evolution. But even the most superficial meaning of Hagalaz is "Negative". Hagalaz means "hail" and hail is a substance consisting of frozen water and air, although it is not as hard or dense as ice; every farmer knows what hail can do to his crops. It is a destructive natural force.
Hagalaz is the uncontrolled forces in the unconscious, which are usually of a disruptive nature and which usually come from the past. Hagalaz signifies the realms of Hel or the underworld, this is the area of the personal unconscious. This rune can be used for the darker side of witchcraft in the negative and feminine sense. The goddess secondarily associated with this rune is "Urd" the oldest of the Norns. It can be used as a spell in a negative nature where it would turn a person's past against them or used to invoke someones Wyrd (Karma).
For magical purposes the "H" stave is most powerful in workings for realization of the structures and dynamics of the "World." It is the seed of knowledge and it is an effective tool for protection.
Brightest of Blessings,