Lucifer's Hammer

Lucifer's Hammer is a post-apocalyptic science fiction novel by Larry Niven and Jerry Pournelle. The story details a cometary impact on Earth that causes the end of civilization as we know it, as well as the struggle to survive in the face of tsunamis, starvation, disease, a new ice age, and an army of cannibals in order to rebuild society.

The story is one of the best of its kind, and was nominated for the 1978 Hugo Award for Best Novel. (It lost to Frederik Pohl's Gateway.) A comic book adaptation was published in 1993. The film Deep Impact was (very) loosely based on it.

Tropes used in Lucifer's Hammer include:

After the End: Unusually for this type of story, the cometary impact doesn't happen until the middle of the story. The last half of the book is all about this trope.
The Apocalypse Brings Out the Best In People: Way, way averted. For the most part, the people who survive the end of the world do so by being selfish, murdering, thieving bastards. Even the "good guys" quickly realize that they can only survive by ignoring most of the people who need help.
Apocalypse How: Planetary/Societal Collapse.
Apocalypse Not: The epilogue.
Apocalypse Wow: Niven and Pournelle take about three chapters in the book to describe the utter destruction of the world, each time detailing the effects of the impact on a different region. In addition, they go to great lengths to describe the effect on the impact on individual characters, some of whom don't survive the experience.
Author Tract: One of the morals of this story is technology (especially nuclear power) is good, while environmentalists and hippies are bad.
But What About the Astronauts?: The multi-national crew of astronauts on the HammerLab (specifically sent up to study the approaching comet) provide a running commentary regarding the approach, and likewise continue to feed information for as long as people keep responding on Earth. When it becomes clear that the space program that put them in orbit is now nothing more than a memory, they decide to return to Earth to see what's left. (Not that they have much choice; their supplies will only last so long....)
Comet of Doom: The Hamner-Brown comet itself. At first, no one thinks it is going to hit the Earth. But then the margin of error keeps getting smaller and smaller....
Cozy Catastrophe: At the end, one of the heroes is celebrating the fact that he and his family (and his friends) have survived the winter, everything's rebuilding, and the future looks bright. Never mind that billions of people are dead and the good guys have effectively organized themselves into a feudal holding...
Depopulation Bomb: The tidal waves caused by the initial cometary impact wipes out most of humanity. In addition, any geological faultlines near an impact site let go completely, causing massive earthquakes and volcano eruptions (and for the purposes of the story, "nearby" means "within a thousand miles") killing most of those who survive the tidal waves. The water vaporized by the oceanic impacts condenses back into rains, causing massive flooding and destroying pretty much any dam still standing after the earthquakes. (Thus drowning people too far away to be killed by the tidal waves.) When you add to this onset of a new ice age caused by nuclear winter conditions, plagues caused by lack of modern medical technology and a shortage of medicine, famine, and the constant danger of bandits, it's a wonder anyone survives to the end of the book at all.
Divided States of America: The survivors, living in and around California's San Joaquin Valley, all make jokes about the five announcements they've received over short-wave radio, each proclaiming a different person President of the United States. The only one they give any level of credence to is the group in Colorado Springs (because a) the person making the proclamation is the former Speaker of the House and thus might actually have legal authority and b) apparently NORAD survived and they still have nukes and working bombers). As far as they are concerned, Arthur Jellison (former US Senator and leader of the effort to organize and rebuild) is their leader. One person says Jellison is 'the Duke of San Joaquin'.
Dramatis Personae: This is a Niven/Pournelle novel, so it has a cast of hundreds. Naturally, there is a list at the beginning of the book in case you get lost.
Earn Your Happy Ending: Where surviving the apocalypse is just the first step.
Fantastic Religious Weirdness: The Reverend Henry Armitage, former radio preacher and post-apocalyptic authentic whack-job, preaches against the evils of trying to rebuild a technological society rather than just accepting God's righteous punishment and allowing humanity to die. Oh, and being a cannibal is okay, if you're on God's mission. People believe him, mainly because they've all committed unspeakable acts and want to believe they've been forgiven.
Heroic Sacrifice: The manner in which Air Force General John Baker saves the nuclear power plant from the cannibal army.
- Taking You with Me also applies to the same scene: "At the Academy, they taught us there was one sure way not to miss..."
Hoist by His Own Petard: A theme of the book. About the only "prepared" survivors, good and bad, who don't have part of their initial schemes blow up in their faces are Senator Jellison and Dr. Dan Forrester.
- The Chinese government gets one of these, mixed with a massive Darwin Award. See Nuke'Em below.
I Did What I Had to Do: With a rapidly climbing threshold as conditions deteriorate. By the end of the book, one generally nice character is justifying slavery.
Jive Turkey: Most of the African-American characters sound like they stumbled out of a 1970s blaxploitation film.
The Last Dance/Dying Moment of Awesome: Gil the Surfer. "If death was inevitable, what was left? Style, only style." And so he decides to surf on the tsunami about to destroy Los Angeles.
- He would have been able to ride that wave as far as it took him (several miles inland) had it not been for an inconveniently placed apartment building. Niven has since stated that, if he was writing the novel now, he would have had Gil the Surfer survive the ride.
Most Writers Are Writers: One of the survivors is a novelist who writes science fiction. Whether he's based on Niven, Pournelle, or a combination of the two is up to the reader to decide.
The Night That Never Ends: In addition to the dust and debris thrown into the upper atmosphere, the massive amounts of water vaporized by the ocean impacts cause a perpetual 100% cloud cover (at one point in the book, it rains for a month) and thus a perpetual twilight. By the epilogue, the skies are clear again.
No Party Like a Donner Party: The remnants of a National Guard unit start off only killing and eating people because they have a hard time finding anything to eat. Later, they descend into I'm a Humanitarian territory, and use forced-cannibalism ("You can eat it, or you can be eaten. Your choice.") as a sadistic recruiting tool, since cannibalism "indelibly marks a person, on their soul", making said persons permanently pariah with any "decent" folk.
Nuke'Em: The Chinese conclude that the Soviets that survive Hammerfall will need to migrate south to avoid future glaciers, and launch a preemptive nuclear attack on the Soviet Union. The (oddly prepared) Soviets immediately use their Nuclear Option and drop their entire Cold War arsenal on China.
- Another "nuclear" option shows up in the climax of the book when the main characters resort to homemade poison gas to stop the increasingly large and motivated cannibal army. The idea is roundly considered horrific but saturating the completely exposed and surprised horde with mustard gas certainly does work...
One Degree of Separation: The novel focuses on characters who all know each other or are related in some way. This helps explain why they are all accepted inside Jellison's ranch when the majority of people who try are turned away. The heroes even know (or at least have met and have some knowledge of) the villains.
Shown Their Work: Extensive and very impressive research means that the cometary impact and its aftereffects are described in brutal, loving detail.
What Happened to the Mouse??: The fate of Charlie Sharps and the JPL staff that followed him is left unknown.