What are the functions of Giantesses in the Norse Mythology and Folklore?

Question

For instance, I recall them being mentioned as the sources of rivers. I'd be interested in more detail on this aspect, as well as any other functions of female jötnar.

(Wikipedia covers this to some degree, but I'm looking for more detailed explanation and analysis, as well as elements absent from the Wikipedia page on the Jötunn, and appearances in folklore outside of the Eddas.)

Answer 1

Jotuns in general served as a sort of the Other for the gods: a group that they used to define themselves by contrast. Female Jotuns were in some senses even more so.

Here is a list of different roles that you could find Jotun women in in myths:

1. Mothers of gods. Almost all major Aesir were born of Jotun women (the only exception I can think of which plays any major role is Baldur).
2. Dangerous disturbers of the established order. One of the stranger parts of the Völuspá is the eight verse, which describes the end of the paradisical past of the gods. The "three maidens" have been suggested to be the Norns, but there is really nothing that can prove this conjecture. The passages following tell how the Gods created dwarves and humans, so this was apparently a huge deal somehow.

In their dwellings at peace | they played at tables,
Of gold no lack | did the gods then know,--
Till thither came | up giant-maids three,
Huge of might, | out of Jotunheim. (quoted from here)

3. Antagonists in stories. You quote them as "sources of rivers". This seems to be the story of how Thor travelled to Geirröd in Þórsdrápa and Skáldskaparmál. On his way, Geirröd sent his daughters Gjálp and Greip to stop Thor. One attempt was by pissing into a river so it overflowed and made it difficult to stop. (Eventually, Thor killed them both)
4. Helpers. In the same story as above, Thor starts by visiting the Giantess Grid which gives him weapons to use (Thor had had to leave his hammer and Belt of strength at home).
5. Avenging daughters. Skadi wanted to avenge her father Thjazi, and went to the gods for reparations (Skáldskaparmál).
6. Goddesses. Skadi is again the major example, she is according to Gylfaginning called "Öndurguð" and "Öndurdís". "Öndur" means "skis", "guð" is "god", and "dis" is an sort of minor goddes (Freya is also sometimes called "Vanadis")
7. Potential wives. Apart form Skadi, there is also the story of how Frey lusted after the giantess Gerðr, and sent the messenger Skrinir to woo her(Skírnismá and Gylfaginning).
8. Beings of supernatural strength. At Balder's funeral, the gods could not made the ship he was to be burnt in to leave the shore, until the giantess Hyrrokkin appeared and launched it -- (Gylfaginning).

Most of these aspects are discussed by Margaret Clunies Ross in Prolonged Echoes. It would be too long to try to expand on each of them, but one of her main arguments is how the Norse myths depicts a society where the Aesir have tried to distance themselves from their giant ancestors, while the giants themselves would like to be put on more equal terms. One of the results of this order is how the Aesir are never married to giant women; it is OK for Vanir like Frey and Njord to marry them, but not Aesir, and the Vanir's marriages do not end well. The Aesir also often uses giantess women when they need children quickly for some tasks, and they have no qualms to seduce and abandon them when they act as guardians of something (a.g. how Odin stole the scaldic mead as told in Skáldskaparmál).

Answer 2

Two very good answers, I just want to point out that the giantesses have a role in religion as well. We know that Jarl Hakon of Norway worshipped the giantess Thorgerdr Holgabrudr, who apparently helped him in battle. (See this pdf file for more on her.) Also, when Skadi and Loki are arguing in the poem Lokasenna, she tells him:

You know, if first and foremost you were at the killing
when you attacked Thiazi,
from my sanctuaries and plains shall always come
baneful advice for you. (51, Carolyne Larrington's translation)

Lotte Motz was a pioneer in studying giants and especially the giantesses. One of her papers, The Divided Image, looks at the way giantesses could be beautiful and desirable or else monstrous.

Answer 3

Basically the same as the Titans in Greek mythology. Just like the Titan Gaia, the Jotunn Jord is Earth herself. Likewise the Celtic goddess Danu is the mother of all life and Earth, she's often depicted as the embodiment of nature pregnant, displaying fertility.

All Indo-European pantheons display the same archetype, that is a dual-pantheon system in which a human-like pantheon of gods, that taught us human things like music and art, magic, military prowess, metal smithing, crop techniques defeated an older pantheon of more primitive/primordial gods, that are usually chaotic, and represent the natural forces that humans don't have control over, storms, snow.

This common mythology themes mirror the Indo-European people's own history, in which from their homeland in the Asian steppes of Kazakhstan they invaded/migrated to new lands and spread their domain all across Eurasia and conquered the inhabitants.

There's this misconception in popular culture (thanks to things like Marvel comics) that giants (Jotunn) are exclusively evil and enemies of the gods and humanity, which couldn't be further from the truth.