Can this underwater air pocket exist? [Archive] - Wizards Community

Can this underwater air pocket exist? [Archive] - Wizards Community

Post/Author/DateTime Post
m o n k
08-13-07, 07:32 PM Hopefully someone here can help me out with this: I'm designing a cave adventure for my players. In one part of the cave, there is a pool of water, and if the pcs decide to swim in the pool they will discover that there is an underwater passage that leads directly to another part of the cave. I am designing a sideview map of the pool and I must say it's looking pretty cool. I want to include an air pocket in part of the cave--kind of a resting place about halfway to the bottom of the underwater cave. That way, if the pcs are adventurous (and a little lucky), they can find the air pocket and rest/catch their breath before they continue to the bottom to find goodies of drowned adventurers.

My problem is that I don't know if air pockets can exist below the water level. I originally drew a tunnel in the wall that curved upward after about 15 feet. Looking at my picture, though, I am beginning to doubt whether that upward space would have an air pocket or just be filled with water.

Any ideas/answers?
shadzar
08-13-07, 07:50 PM with sufficeint pressure and no where else for air to go it can form a pocket in some space under the water. at least so cartoon and movies have shown us.

how the air got there or if it is breatheable is up to you.

you jsut need some space for the air to occupy rather than just just along a seemingly flat surface of a tunnel otherwise the air would have long since escaped.
Kensan_Oni
08-13-07, 08:08 PM As long as you have a catch for the air to prevent it from going anywhere, and the pressure of the water is not too great (I think you're fine there, from the sounds of things), you can have pockets of air almost anyplace. The real question is if it will be breathable air, and the hazards of D&D mildew... but that's a question you need to answer for yourself.
m o n k
08-13-07, 08:16 PM Cool. Thanks!
Windbit
08-13-07, 08:44 PM Stormwrack has a spell called Airy Water that you might be interested in. It creates an area of bubbly water that both air breathers and aquatic creatures can breath in, as well as allowing both normal land speed to walk on the bottom and swim speed.
supernerd222
08-13-07, 08:47 PM I agree with the first two posts on the condition that the cave came before the water. That is to say, there was a hole in the ground and water somehow got into it, thus filling it from the bottom up.

However if the cave was formed through another mehod, such as water rushing through the system in wintertime, eroding until it forms the pool that is present, then being insulated from permeable ground and sunlight, trapping the water in place. In other words, if the water made the cave. If this is the case, an air bubble would be impossible, because water cannot flow uphill, and therefore cannot erode the ceiling to make a place for air to sit. And even if it could, where would air come from? The exception to this would be if the water made the cave, but has exited at some point since, then come back, because in the water's absence a chunk of rock could come off the ceiling, or on a larger scale, a stalactite curtain could form, creating an air trap as described above.

The problem is, the vast majority of caves are made from water eroding rock, gradually making a hole, which is the second scenario, the one that makes it really hard for air bubbles to exist. And if the water has left in the past, facilitating the existance of an air bubble, what factor is preventing it from leaving now? Perhaps a series of dry winters led to the very gradual evaporation of the water, but that weather pattern has ended.

I'm probably overcomplicating things to all hell. Just put the air bubble in. I mean, what kind of player says, "Hey, an air bubble in a cave clearly formed by water erosion! Dude, that completely violates the laws of fluid dynamics," anyway?
m o n k
08-13-07, 08:55 PM No, I appreciate you thinking it through. I get how a cave filling with water could have the air pocket I desire.

I'm sure now that I've thought it through and gotten your help, my players will be too cautious to explore the pool. Maybe I'll have them see a faint glow in the pool. By the time they realize it's just bioluminescent aquatic cave moss, they'll have seen the route to the other section of the cave.
shadzar
08-13-07, 09:12 PM just as long as they don't eat that moss they will be fine.
lulzapalooza
08-13-07, 09:30 PM Just do it! It's a cool idea, and your players will enjoy it. If one of them says, 'thats not possible' say, "I thought of that, but I figured I'd throw you a bone, but since you want realism, what's you're constitution? You're in danger of drowning."
Sarella Starshine
08-13-07, 09:42 PM Or, you can always go by the default 'it's magic' route. If the players *really* want to investigate why an air pocket exists in this cave when logic says its impossible, make it an adventure hook :).

But, in the real world, air pockets do exist in underwater cave system. Of course, the further down you go, the less likely they exist (water pressure mentioned above), but even then, that is no reason not to have one being somehow magically sustained.
Schemerrat
08-13-07, 09:49 PM It's your cave, in a magical world :D

if you want to, just stick a big bubble of air to the bottom of the lake, you just have to use some magical DM-glue to keep the air-elemental in place :P
Luis_Carlos
08-14-07, 03:53 AM In the cosmology from my own setting what I´m creating there is Aquaeter, a fictional liquid what is totally incorporeal (but with the water). Then it´s seems a air bubble in the deepest from sea, but really is almost solid meta-matter. Sea elfs and other creatures (like sea mammal) use it to living there.

I have too the option the aquaeter is totally solid for fishs, and the predator like sharks can "fly" in the "air bubbles" of aquater to hunting.
Neutronium_Dragon
08-14-07, 07:07 AM The primary problem with having trapped air from when it originally filled up is that the air probably won't be all that good by now - and it certainly won't last very long once the PCs start breathing it even if it is.

If you assume that the spot where the air is trapped was already there (even carved by the water), you could have some small fissure in the rock below (as long as your map doesn't need the space below!) which is emitting air bubbles at a slow pace - enough to create that pocket and to send the occasional bubble further up the cave (where it eventually breaks the surface of the pool). This would also allow the pocket to be refreshed (although they'd still better not spend too long there).
konrad_the_tall
08-14-07, 07:16 AM Agreed. Its your world. **** the laws of pychics.

Post/Author/DateTime	Post
m o n k 08-13-07, 07:32 PM	Hopefully someone here can help me out with this: I'm designing a cave adventure for my players. In one part of the cave, there is a pool of water, and if the pcs decide to swim in the pool they will discover that there is an underwater passage that leads directly to another part of the cave. I am designing a sideview map of the pool and I must say it's looking pretty cool. I want to include an air pocket in part of the cave--kind of a resting place about halfway to the bottom of the underwater cave. That way, if the pcs are adventurous (and a little lucky), they can find the air pocket and rest/catch their breath before they continue to the bottom to find goodies of drowned adventurers. My problem is that I don't know if air pockets can exist below the water level. I originally drew a tunnel in the wall that curved upward after about 15 feet. Looking at my picture, though, I am beginning to doubt whether that upward space would have an air pocket or just be filled with water. Any ideas/answers?
shadzar 08-13-07, 07:50 PM	with sufficeint pressure and no where else for air to go it can form a pocket in some space under the water. at least so cartoon and movies have shown us. how the air got there or if it is breatheable is up to you. you jsut need some space for the air to occupy rather than just just along a seemingly flat surface of a tunnel otherwise the air would have long since escaped.
Kensan_Oni 08-13-07, 08:08 PM	As long as you have a catch for the air to prevent it from going anywhere, and the pressure of the water is not too great (I think you're fine there, from the sounds of things), you can have pockets of air almost anyplace. The real question is if it will be breathable air, and the hazards of D&D mildew... but that's a question you need to answer for yourself.
m o n k 08-13-07, 08:16 PM	Cool. Thanks!
Windbit 08-13-07, 08:44 PM	Stormwrack has a spell called Airy Water that you might be interested in. It creates an area of bubbly water that both air breathers and aquatic creatures can breath in, as well as allowing both normal land speed to walk on the bottom and swim speed.
supernerd222 08-13-07, 08:47 PM	I agree with the first two posts on the condition that the cave came before the water. That is to say, there was a hole in the ground and water somehow got into it, thus filling it from the bottom up. However if the cave was formed through another mehod, such as water rushing through the system in wintertime, eroding until it forms the pool that is present, then being insulated from permeable ground and sunlight, trapping the water in place. In other words, if the water made the cave. If this is the case, an air bubble would be impossible, because water cannot flow uphill, and therefore cannot erode the ceiling to make a place for air to sit. And even if it could, where would air come from? The exception to this would be if the water made the cave, but has exited at some point since, then come back, because in the water's absence a chunk of rock could come off the ceiling, or on a larger scale, a stalactite curtain could form, creating an air trap as described above. The problem is, the vast majority of caves are made from water eroding rock, gradually making a hole, which is the second scenario, the one that makes it really hard for air bubbles to exist. And if the water has left in the past, facilitating the existance of an air bubble, what factor is preventing it from leaving now? Perhaps a series of dry winters led to the very gradual evaporation of the water, but that weather pattern has ended. I'm probably overcomplicating things to all hell. Just put the air bubble in. I mean, what kind of player says, "Hey, an air bubble in a cave clearly formed by water erosion! Dude, that completely violates the laws of fluid dynamics," anyway?
m o n k 08-13-07, 08:55 PM	No, I appreciate you thinking it through. I get how a cave filling with water could have the air pocket I desire. I'm sure now that I've thought it through and gotten your help, my players will be too cautious to explore the pool. Maybe I'll have them see a faint glow in the pool. By the time they realize it's just bioluminescent aquatic cave moss, they'll have seen the route to the other section of the cave.
shadzar 08-13-07, 09:12 PM	just as long as they don't eat that moss they will be fine.
lulzapalooza 08-13-07, 09:30 PM	Just do it! It's a cool idea, and your players will enjoy it. If one of them says, 'thats not possible' say, "I thought of that, but I figured I'd throw you a bone, but since you want realism, what's you're constitution? You're in danger of drowning."
Sarella Starshine 08-13-07, 09:42 PM	Or, you can always go by the default 'it's magic' route. If the players really want to investigate why an air pocket exists in this cave when logic says its impossible, make it an adventure hook :). But, in the real world, air pockets do exist in underwater cave system. Of course, the further down you go, the less likely they exist (water pressure mentioned above), but even then, that is no reason not to have one being somehow magically sustained.
Schemerrat 08-13-07, 09:49 PM	It's your cave, in a magical world :D if you want to, just stick a big bubble of air to the bottom of the lake, you just have to use some magical DM-glue to keep the air-elemental in place :P
Luis_Carlos 08-14-07, 03:53 AM	In the cosmology from my own setting what I´m creating there is Aquaeter, a fictional liquid what is totally incorporeal (but with the water). Then it´s seems a air bubble in the deepest from sea, but really is almost solid meta-matter. Sea elfs and other creatures (like sea mammal) use it to living there. I have too the option the aquaeter is totally solid for fishs, and the predator like sharks can "fly" in the "air bubbles" of aquater to hunting.
Neutronium_Dragon 08-14-07, 07:07 AM	The primary problem with having trapped air from when it originally filled up is that the air probably won't be all that good by now - and it certainly won't last very long once the PCs start breathing it even if it is. If you assume that the spot where the air is trapped was already there (even carved by the water), you could have some small fissure in the rock below (as long as your map doesn't need the space below!) which is emitting air bubbles at a slow pace - enough to create that pocket and to send the occasional bubble further up the cave (where it eventually breaks the surface of the pool). This would also allow the pocket to be refreshed (although they'd still better not spend too long there).
konrad_the_tall 08-14-07, 07:16 AM	Agreed. Its your world. **** the laws of pychics.