Valeria's Minor Gateway

The caster draws in the air a portal or doorway which then briefly opens to one of the four elemental planes, letting the raw energy and material of the plane flow into the world. The portal opens for only a second or two. The back of the portal appears as a transparent wall but is not solid and can be passed through (except when the portal is connected to the Plane of Earth), though this is discouraged as you may be affected by whatever came through the portal.

Plane of Fire: When the portal opens, a half sphere of heat and energy bursts forth, enveloping everything within 20 foot in flames and dealing 8d6 points of fire damage. Creatures in the area of effect can make a Dexterity saving throw for half damage.

Plane of Air: A strong gust of fresh air rushes out, blowing over anything not firmly attached to the ground. Creatures within 20 feet must make a Strength saving throw to stay on their feet. If there is nowhere for the air to go, for example if the portal is opened in a sealed room, the pressure in the room raises, but there is no wind. If opened in a hallway or other restricted space the effects are intensified, possibly knocking creatures back.

Plane of Water: 3000' cubic feet (30 x 10 x 10) of fresh water burst forth from the portal. Like a portal to the plane of air, the effects are largely determined by the terrain the portal is opened into.

Plane of Earth: Considering that the plane of earth is solid material, this spell effectively creates a very short lived solid wall.

There is a very small, but non-zero, chance that the portal opens near a denizen of the plane, which may accidentally or intentionally be swept through the portal and into existence. This creature is not bound in any way. DMs should be careful in deciding if and what ever comes through the portal.

A portal drawn at half the size would produce ¼ the volume, so a halfling opening a portal to the Plane of Water would produce 1500 cubic feet of water.