At the Lost World Safari yahoogroup, there have been some excellent suggestions about modelling tar pits and other pre-historic style terrain including land slides, hot springs, choking gasses and other nasties. I guess hunting 30 foot carnivorous beasts just wasnt dangerous enough!
"In our Lost World type game (see http://www.morvalearth.co.uk/Lost%20World/Lost_Wld_gal_01.htm and http://www.morvalearth.co.uk/Claymore05/balloonatic_intro.htm ) we had a number of "natural" occurrences on cards.
That flat ground is a thin crust that gives way underfoot. Select a party member at random. Gets stuck in it and it takes a score of 8+ on a d10 to free them. Add 1for each additional person helping. Add more if they are using ropes, overhead in a balloon etc. These assistants may not shoot or fight this turn. A roll of 1 means that the victim is slowly immersed in tar and choking and baking dies a horrible death.
A mist envelops the party. It blocks sight and reduces movement by half. Roll d6:
1,2 it lasts 3 turns
3,4 it lasts 2 turns
5,6 it lasts 1 turn
Roll d10 for each figure. If a 1 is rolled on any turn that figure is lost. When the mist clears roll a d6 for each turn the figure was lost and move away from their party in a random direction that number of inches.
A sudden jet of hot gas blasts from the ground. One random figure is knocked over and loses his/her weapon on a d10 roll of 1-3. The weapon may be recovered next go if they roll 7+
That flat ground is a thin crust that gives way underfoot. Select a party member at random. Falls in and it takes a full turn to free them.
A sudden geyser of hot water blasts from the ground. One random figure is knocked over and so is the one following him. They lose their weapons on a d10 roll of 1-3. The weapon may be recovered next go if they roll 7+
The cliff nearby gives way. D6 boulders bounce towards the party. Roll a d10 for each member within 9” needing 2+ to hit less one on the die per inch the boulder travels.