Related by context. All words. (Click for frequent words.) 70 Huge plumes 68 Thick black 67 Thick plumes 61 dust billowed 61 plumes 60 gray smoke billowed 58 thick plume 58 intermittent artillery shelling 57 Smoke billowed 56 Billowing clouds 56 Acrid black 55 smoke billowed 55 Dense clouds 54 smoke plumes 54 smoke wafted 54 Thick smoke 54 acrid black 53 Thick clouds 53 thick plumes 53 roiling plume 53 ash billowing 52 gray smoke billowing 52 plume 51 spews ash 51 Flares lit 51 smoke belched 51 Gadhafi sprawling Bab 51 thick pall 51 billowing clouds 51 orange fireballs 50 thick smoke billowed 50 volcano spewed ash 50 Mount Merapi spews 50 acrid smoke billowed 50 Icelandic volcano spitting 50 Shajaiyeh section 50 Ras Lanouf blazing 50 Thunderous explosions 50 clouds billowed 50 Explosions shook 50 Smoke 50 billowing 49 black smoke billowed 49 Billowing 49 billowing plume 49 Grímsvötn volcano 49 glowing lava 49 high explosive airbursts 49 clouds billowing 49 Indonesia volcano spews 49 Thick smoke drifted 49 grayish ash 48 smoke billows 48 acrid smelling smoke 48 Indonesian volcano spews 48 white hued multistory 47 Explosions rocked 47 Smoke rises 47 Loud explosions 47 towering plumes 47 smoke billow 47 streaking diagonally 47 Wafts 47 towering plume 47 Palls 47 smoke plumed 47 Clouds 47 flames billowed 47 steam billowed 47 volcanic ash originating 47 spews lava 47 belched ash 46 billowing plumes 46 Kawangware slums 46 billowing smoke 46 billows 46 Volcano spews 46 Towering plumes 46 Acrid 46 spewed plumes 46 ash spews 46 Billowing smoke 46 al Aziziya compound 46 billowed 46 clouds billow 46 Burned corpses 46 Black smoke billowed 46 tracer bullets sliced 46 warplanes streaked 46 smoke wafting 46 smoke billowing 46 belched clouds 46 Philippine volcano spews 46 Halema'uma'u 46 NEAR MARJAH Afghanistan 46 Smoke billows 46 Military helicopters hovered 45 Beit Lahiya Beit Hanun 45 Ambulances streamed 45 Acrid smoke 45 Spews Ash 45 Bursts 45 volcano spews ash 45 sending palls 45 El Chichon 45 Lava flows 45 streaking diagonally across 45 Helicopters patrolled 45 Cotinus 45 noisily overhead 45 BP.com website early 45 billow 45 Smoke billowing 45 haze enveloping 45 Tracer bullets 45 Montserrat volcano 45 twisting alleyways 44 Seeping 44 Ecuador Tungurahua volcano 44 Ambulances raced 44 billowing cloud 44 Spills Into 44 smoldering fuselage 44 Mishahda north 44 St. Helens belched 44 Heavy gunfire 44 Soot 44 Chile Chaiten volcano 44 warplanes roared 44 gigantic sparklers lit 44 Lightning flickered 44 sky glowed 44 fireball streaking 43 Mount Cudi 43 Halemaumau crater 43 tetrachloroethene PCE 43 glowed orange 43 Volcano spews ash 43 refinery torches belched 43 acrid smoke billowing 43 convulsing earth 43 Sporadic gunfire 43 Muzzle flashes 43 gunfire resounded 43 explosions boomed 43 smoke 43 raid sirens wailed 43 Veniaminof 43 Mount Merapi spewed 43 Thick sticky 43 Dense smoke 43 swirling sandstorm 43 sulphurous smell hung 43 Philippines Mayon volcano 43 tracer bullets streaked 43 Azizia compound 43 Boom billows 43 lungs Setree 43 Erupting 43 lava flowed 43 Iceland Eyjafjallajoekull volcano 42 Thick smoke poured 42 Ecuador Tungurahua 42 Explosions boomed 42 foamy bubbles 42 Tarballs 42 erupting lava 42 acrid smoke 42 Flares 42 zero halogen 42 Ethiopian helicopter gunship 42 Swirling 42 Towering clouds 42 Force Evacuations 42 black smoke billowing 42 Thunderous explosions rocked 42 blue domed mosque 42 Russia Kamchatka volcanoes 42 haze blurs 42 volcano spews lava 42 Mount Shinmoedake 42 pancake batter suffocates grasses 42 predawn sky 42 Grimsvotn erupted 42 volcanic cliffs 42 smokestacks belching 42 fiery lava 42 spew lava 42 sperm whales gigantic 42 helicopters clattered 42 Wafting 42 Indonesian Volcano Spews 42 Indonesia Merapi volcano 42 underground inundates 42 wisps 42 Volcano Erupts 42 dusty haze 42 Kamoamoa eruption 42 Recriminations erupt 42 produce sooty acrid 42 fighter jets thundered 42 UFO hovering 42 Iceland Eruption 42 Mount Karthala 42 Mariana Arc 41 Gunfire reverberated 41 gunsmoke 41 lava fountains 41 Swirls 41 Grimsvoetn volcano 41 Ominous clouds 41 Mount Sinabung spews volcanic 41 Odaiba district 41 Perseus constellation 41 Gunshots echoed 41 Fireworks thundered 41 rattling conveyor belts 41 blue wool crepe 41 Gunfire crackled 41 Mount Merapi spews volcanic 41 ash cloud drifted 41 Forces Evacuations 41 Eyjafjallajökull glacier 41 quaint crescent 41 Augustine Volcano 41 Alaska volcano erupts 41 grayish smog blotted 41 helicopters circled 41 La Cumbre volcano 41 Baiyaa religiously mixed 41 irregular eruptions 41 Mount Galunggung 41 spewing plumes 41 purple bougainvillea 41 moonless sky 41 Ust Kamchatsk reducing 41 Gunfire rang 41 Machinegun fire 41 flames billow 41 Hundreds Flee 41 burning plastic Rymarev 41 Explosions reverberated 41 Microscopic particles 41 al Shurta 41 mushroom cloud 41 clouds 41 fog blanketed 41 Fiberglas fabric roof 41 magma dome 41 gigantic Luzhniki Stadium 41 Radiation readings 41 haze shrouded 41 Thousands Evacuated 41 Kirishima range 41 Explosions 41 Scattered clouds 41 belched plume 41 rainbow arched 41 Huge explosions rocked 41 constellation Leo 41 energetic electrons 41 Leak Causes 41 Erupts 41 acrid haze 41 misty fog 41 plume drifting 41 flickering strobe lights 41 spewing volcano 41 flames leaping 41 Dai ichi nuclear 41 Explosion Heard 41 Gunfire rattled 41 clouds scudding across 40 ash spewed 40 azure 40 Laki volcano spewed 40 Mayon crater 40 clanking cans 40 AP Photo LEFTERIS 40 Explosives Packed 40 Barrages 40 Alaska Augustine Volcano 40 ionized hydrogen 40 leaden gray 40 Pu ` 40 Halemaumau Crater 40 Helicopters buzzed 40 Washes Up 40 Mosecomonitoring watchdog agency 40 meteor streaks 40 Smoke wafted 40 Ingame Description Attack 40 welding sparks 40 spitting embers 40 Eyjafjoell volcano 40 Pipeline Explodes 40 Polish flags fluttering 40 Wisps 40 uninhabited Vatnajokull glacier 40 volcano spews 40 Bomb Plotters 40 Snowy Egrets 40 shaggy goats 40 Helicopters hovered 40 gases vapors 40 Warplanes Strike 40 resembled rust colored 40 Sectarian tension 40 Sporadic explosions 40 spewed ash 40 brownish haze 40 Apache helicopters circled overhead 40 Sporadic shelling 40 Explosions Heard 40 de Poche 40 Waterspouts 40 Scuba divers donned flippers 40 Claymont Del. spilling 40 lava oozing 40 clouds scud 40 Sumbawa Island under 40 hurling fireball 40 Redoubt volcano 40 Nyiragongo volcano 40 Rocket propelled grenades 40 Multicolored starbursts 40 Pu'u O'o 40 Smoke pours 40 Celebratory fireworks 40 grayish white 40 SEVERE THUNDERSTORMS WILL BE 40 irritant potassium hydroxide 40 Kilimanyoka 40 Death Toll Continues 40 Eyjafjallajoekull glacier 40 reddish glow 40 aka ssa 40 Boyong rivers 40 dun colored 40 greenish yellow 40 volcanic ash drifts 40 Basra Hananiyah neighborhood 40 prized Shiite shrine 40 Eyjafjallajokull Iceland 39 belching smoke 39 Sewage Leak 39 Iceland Grimsvoetn volcano 39 Yokohama Isogo area 39 Polycyclic aromatic hydrocarbons 39 detritus perched 39 sky 39 Causes Evacuations 39 clouds scudded 39 sporadic gunfire echoed 39 Rescuers combed 39 Found Near 39 Blown Tire 39 black smoke billow 39 Puu Oo 39 Prompts Evacuation 39 Tensions 39 Foul smelling 39 Polycyclic Aromatic Hydrocarbons 39 Hundreds Evacuated 39 carbon monoxide nitrogen oxides 39 Artillery shells 39 Injure Dozens 39 deforested mountains 39 Perseus Cluster 39 underwater plume 39 helicopters hovered 39 Fireworks exploded 39 Sistine Chapel chimney 39 Explosion Shakes 39 constellation Aquarius 39 Squawking seagulls 39 Explosions rang 39 Fierce clashes raged 39 haze blanketing 39 spewed lava 39 Concentrations 39 Contrails 39 Truck Bomber Kills 39 Thick smog 39 orange glow 39 Merapi Volcano 39 acrid aroma 39 Charred bodies 39 waterpipes 39 Contaminates 39 clouds loomed 39 spectacular lightning crackled 39 Askariya mosque compound 39 pink bougainvillea 39 Shinmoedake 39 resemble moonscape 39 tsunami stricken Fukushima 39 Worse Than Thought 39 traps pelicans 39 cumulus cloud 39 tracer bullets 39 constellation Carina 39 Insurgent Stronghold 39 Wildfire Near 39 Rebel Stronghold 39 craggy hills 39 billowing brown 39 Bunker Busters 39 Llaima volcano 39 thin crescent 39 Mount Bulusan 39 Eruptive activity 39 dense volcanic ash 39 La Soufriere 39 propelling steaming blobs 39 Fireworks lit 39 Arsia Mons 39 QUITO Ecuador Ecuador Tungurahua 39 Shajaiyeh neighborhood 39 Helicopters clattered 39 bleak steppes 39 Partial lunar eclipse 39 Astronomers Find 39 Blast Hits 39 Qlaiah 39 Clashes Erupt 39 bunting hung 39 Aadhamiya district 39 Missing Fisherman 39 thunderclouds 39 Lava spews 39 dusty alleyways 39 irritate airways 39 benzene arsenic 39 volcanic plume 39 cobblestone alleyways 39 melted glacial 39 Globs 39 Perseid meteor showers 39 constellation Virgo 39 sirens wailing rushed 39 Grimsvotn GREEMSH votn volcano 39 Forces Evacuation 39 cotinine metabolite 39 eruption Redoubt sent 39 Eyjafjallajokull Volcano 39 charred tree trunks 39 Disrupts Flights 39 Dwarf Galaxies 39 raining ash 39 unstable lava dome 39 Jolan district 39 Shiveluch 39 Volcano erupts 39 Explosion Damages 39 rfoster@nwherald.com 39 Icelandic volcano drifted 39 Sporadic bursts 39 Traces 39 smoke wafts 39 Engulfs 39 Explosions thundered 39 mist 39 Tanah Karo 39 Gunshots rang 39 Krakatoa volcano 39 nail spreader 39 Car Bombings 39 cumulous clouds 39 Diesel Spill 39 Thousands Flee 39 constellation Hydra 39 Tin roofing 39 glass crunched underfoot 39 clouds obscuring 39 Grounds Flights 39 Debris 39 Mount Krakatoa 39 winged lions 39 -4 Fahrenheit 39 Trifid 39 ambulances raced 39 Threatens Homes 39 lava fragments 39 called zorbs 39 Sporadic gunfire echoed 39 Suspicious Object 39 Wind Whipped 39 Jokhang temple Ramoche monastery 39 unmarketable byproduct 39 gray taupe 39 Prompts Evacuations 38 flames billowing 38 TCE trichlorethylene 38 drift lazily 38 chimneys belching 38 haze shrouding 38 Alaska Mount Redoubt 38 lava trickling 38 pyroclastic surges 38 Halemaumau 38 ash spewing 38 Saturn moons Titan 38 spillway diverts river 38 helicopter gunship patrolled 38 gunfire reverberated 38 grazing Inge 38 Rebel Positions 38 Helicopters clattered overhead 38 Pyroclastic flows 38 leaden sky 38 Warplanes Hit 38 F# warplanes 38 Mount Nyiragongo 38 flames everywhere Faizi 38 Human Remains Found 38 Fierce Clashes 38 Destroys Homes 38 Al Shalchi contributed 38 Gunfire 38 blackish 38 Kikuyus Kibaki 38 exhales cloud 38 faint wisps 38 constellation Scorpius 38 Grimsvötn volcano 38 towering peaks 38 incense wafted 38 fissure eruption 38 Smouldering 38 methyl isocyanate gas 38 Redoubt Volcano 38 sandbagged emplacements 38 Kilauea caldera 38 Sporadic rocket 38 spewing searing 38 inky blackness 38 Warplanes Bomb 38 Lake Vui 38 thick haze 38 rust colored slick 38 Arson Blamed 38 Suspicious Device 38 towering geyser 38 Hubble Captures 38 Eludes Capture 38 Sulawesi island chain 38 Deadly Bombing 38 secessionist sentiment 38 Bug Nebula 38 Puu Oo vent 38 containing soot dioxins 38 Loud explosions rocked 38 aftershocks rumbled 38 Berwyn Mountains 38 red tracer bullets 38 Prompts Debate 38 Iqraa bookstore 38 Kosovska Mitrovica Serb 38 rattled tin roofs 38 spokesman Masateru Araki 38 banners fluttered 38 Washes Ashore 38 Scientists Iceland Grimsvotn 38 am Guchhait 38 volcano spewed clouds 38 crunches underfoot 38 Manholes 38 Pipeline Explosion 38 Tanker Explosion 38 smoker vents 38 Hydrogen Sulfide 38 raid sirens sounded 38 Warplanes Pound 38 Causes Power Outage 38 onlookers gaped 38 Carefully cautiously 38 desert squinting 38 star Spica 38 Shiveluch eruption 38 waterfall cascades 38 Jeff Juzyk looked 38 blackish gray 38 Unrest spreads 38 barren smoky wasteland 38 Grímsvötn 38 Icelandic volcanologist 38 Mailboxes barely 38 Syrtis Major 38 OUR LENS 38 skyscraping Ukraina Hotel 38 Grimsvotn 38 Gunshots 38 thin wisps 38 belching steam 38 Ibl el Saqi 38 gleaming towers 38 orange flames licked 38 flattened thatch roofed 38 al Taf 38 Multicolored starbusts 38 Soot particles 38 Mount Karangetang 38 Roiling 38 Forces Seize 38 Breathtaking views 38 gigantic fireball 38 Acre Wildfire 38 wafting 38 Argument Ends 38 blasts sirens wailing 38 Natori river 38 Mich. hookah fanciers 38 Deadly clashes 38 smoggy haze 38 Erupts Into 38 Bushfire toll 38 Battle Rages 38 Fierce battles 38 Gendol River 38 rocky crevices 38 wings Rusdi local 38 limestone cliff 38 Launches Airstrike 38 Tanker Overturns 38 Grimsvoetn 38 tiled rooftop 38 commander Shirin Agha 38 Snow flurries 38 Explosive eruptions 38 Causes Flooding 38 Scientists Warn 38 Documentary Feature Deliver Us 38 Cameraman Killed 38 van Arkel discovery 38 Khaki Jabar district 38 wooded ridges 38 Ammo Dump 38 snipers perched 38 pillowy clouds 38 Volcano Spews 38 gave Beijingers respite 38 Ellipse sprayed gray 38 Causes Evacuation 38 flames licked 38 oily brown pelicans 38 Authorities clamped curfew 38 Cassini Finds 38 expletive laden chats 38 Waterspout 38 engorged river 37 mushroom shaped 37 particulates sulfur dioxide 37 smoldering ashes 37 geologist Jennifer Adleman 37 Iceland spewing 37 Untreated sewage 37 Rips Through 37 Corona Australis 37 Glendale Pasadena 37 Bulusan volcano 37 orangish 37 horseshoe shaped crater 37 Kilauea summit 37 Automatic FI Dark 37 thunderous explosions 37 Tear gas 37 butterfly weed Asclepias 37 ash Sha'b 37 constellation Eridanus 37 conical dome 37 Lava Flows 37 drenching rain raked 37 vapor trails 37 pyroclastic 37 funnel cloud darkened 37 Taints 37 sending billowing clouds 37 charred hulks 37 carbon monoxide particulate matter 37 YOU ARE ENTITLED TO 37 benzene ethylbenzene 37 rotating counterclockwise 37 soot McPhee 37 Wreckage Found 37 Prompts Closure 37 al Salhiya 37 Catalytic Converter Thefts 37 volcano spewed 37 Chunks 37 Midafternoon Trading 37 starlike object 37 reactor Tohoku Electric 37 Snaking 37 Fireballs lit 37 helicopters buzzed 37 rainbow colored sheen 37 Dark clouds 37 fireworks crackled 37 Explosion Reported 37 robes chanted 37 Mount Soputan 37 Soyuz heavenward atop 37 Photographer Captures 37 polyaromatic hydrocarbons 37 Spontaneous celebrations 37 Reilly Plating Co. 37 Pollution Levels 37 Sunlight streams 37 incense wafts 37 tornado flinging 37 sulfurous smell hung 37 Advisory Lifted 37 Vatnajokull glacier 37 PALO DURO Water 37 Foreboding 37 ist raus 37 belching clouds 37 Hovers Over 37 trichloroethene TCE 37 Traces Found 37 Fireworks explode 37 Engulfing 37 fog envelops 37 Emits 37 Mount Tambora buried 37 pinon pines 37 cumulonimbus 37 Truck Blast Kills 37 mists 37 thick globs 37 lava oozed 37 sulfurous steam 37 Gunshots Fired 37 Homes Evacuated Near 37 Smashes Through 37 Ethnic tensions 37 sooty particles 37 Helicopters swooped 37 ooze naturally 37 Norman Paech awoke 37 Shattered glass 37 Dissipating 37 moisture condenses 37 Man Rescued 37 Asteroid Belt 37 Cloudier 37 Outback grit 37 Gasoline Stockpiles 37 Raises Stink 37 steam vents 37 Residents Flee 37 deafening thunder 37 Grimsvotn volcano Iceland 37 Darkened 37 Death Toll Rises 37 Coma Berenices 37 Mortar Attacks 37 spewing radioactive 37 Unrest Spreads 37 altocumulus 37 drifting southwards 37 Wind Advisories 37 pyroclastic flow 37 Brushfires 37 Gasps 37 fiery sunsets 37 Fire Extinguished 37 cloudy dispersant 37 Washing Ashore 37 Organ Pipes 37 blackened skies 37 volcano belched 37 aka jro 37 Rouba Kabbara 37 Eyjafjallajoekull 37 Explosion Destroys 37 blade jutted 37 www.ind.homeoffice.gov.uk 37 brushy canyon lands 37 yer kuh duhl volcano 37 lava spewing 37 Sectarian clashes 37 Advisories Issued 37 arsenic benzene 37 Detonations 37 marble paving stones 37 Thieves Stealing 37 flares anew 37 explosions resounded 37 Loud booms 37 ATTACKS IN 37 Colima volcano 37 airfield bursting 37 Gamma ray bursts GRBs 37 Ashtrays 37 trickling fountains 37 Roadside Bombs 37 Fresh globs 37 Retardant 37 Stampede Kills 37 Cosmic rays 37 darkening sky 37 rooftops 37 Roadside Bomb 37 purple heather 37 moon Mimas 37 Evacuated Due 37 undersea volcanoes 37 An APTN cameraman 37 acrid fumes 37 DD3 toward 37 Down Embankment 37 See TIME photoessay 37 ashy gray 37 volcanologist Agus Budianto 37 volcano lava dome 37 OR DISAPPROVED THE 37 Haret Hreik neighborhood 37 Razed 37 Cleanup Continues 37 Portents 37 savaged Joplin 37 fumaroles 37 siliceous sediments 37 ash plumes 37 smokey haze 37 glowing brightly 37 THEMIS Image 37 Causes Scare 37 screaming Ukhtai 37 Corpse Found 37 loud explosions 37 Balad Dujail 37 Causes Panic 37 Popular uprisings 37 dioxins furans 37 mossy green 37 silhouetting Gaza tall 37 drifting westward 37 Peterson Elvira Mistress 37 Peach Blossom Mountain 37 Raw Sewage 37 winding alleys 37 sun glistened 37 Roars Through 37 northern arctic plains 37 Causes Massive 37 Bathed 37 Burning Apartment 37 Suicide Bombs Kill 37 thin wispy clouds 37 searing clouds 37 scudded 37 Storms Threaten 37 Molten lava 37 Sespe Condor Sanctuary 37 Nicotine Levels 37 Snuffs Out 37 Survivor Recalls 37 airship exploded 37 Blasts Hit 37 Troops Seize 37 smoky aromas 37 Truck Carrying 37 constellation Auriga 37 SoCal Wildfire 37 Wildfires Continue 37 Chicxulub Crater 37 Dissipates 37 Splintered wood 37 slender minarets 37 Fighting Intensifies 37 Firehole River 37 Art pilsner beers 37 slick sprayer 37 Bus Bombing 37 Pu'u O'o vent 37 Leak Shuts Down 36 convective clouds 36 puffy clouds 36 Sector Snap Semiconductors 36 Fierce gunbattles 36 Clouds obscured 36 Explosion shakes 36 Shards 36 powdery sand 36 Melting Glaciers 36 majestic brown pelicans 36 Crews Respond 36 armored vehicles maneuvered 36 Warplanes Attack 36 majestically 36 SAM RAYBURN Water 36 Spews 36 Fatal Blast 36 Sirens wailed 36 Fighter Jet Crashes 36 twisting alleys 36 Sustained gunfire 36 Homemade Bomb 36 crater gouged 36 Blasts Shake 36 Afghan Civilian Deaths 36 sulfuric dioxide 36 solitary slender 36 Conflict Escalates 36 helicopter gunships circled 36 Car Bomb Blasts 36 Truck Bomb Kills 36 Beehive Cluster 36 Desertions 36 rhythmic whoosh whoosh whoosh 36 Attackers detonated 36 Storm Weakens 36 Bait Hanun 36 Firefighting Efforts 36 acrid tear 36 Bernard Celier spokesman 36 LHF Seven Summits Strategic 36 RS Ophiuchi 36 Death Toll Climbs 36 al Askariya mosque 36 palls 36 Mortar shells 36 Spy Drones 36 Battle Erupts 36 Wreckage 36 Unrest Continues 36 Strikes Kill 36 Stoking bullish sentiment 36 clifftops 36 flags flapped 36 Vortices 36 Rig Blast 36 flags banged tambourines 36 Seat #D 36 erupting Iceland volcano 36 Sicily Mount Etna 36 flags fluttered 36 Tar Balls 36 blue burqas trickled 36 Deadly Blast 36 barred spiral galaxy 36 Pollutants 36 delicate coastal marshes 36 smoky 36 Fairport Harbor lakefront 36 Blast Destroys 36 BIGUS 36 Reportedly Kills 36 craggy peaks 36 Militants Clash 36 Typhoon Durian blasts 36 Appearance Pours 36 boulders cascaded 36 poppy petals 36 Adjame neighborhood 36 BELIEFS PLANS EXPECTATIONS AND 36 Virgo Cluster 36 inky shadows 36 Indonesia Mount Merapi 36 hilltops 36 Blast Rocks 36 Israeli warplanes retaliating 36 began unleashing torrents 36 Causes Damage 36 Hangs Over 36 Explosion Rocks 36 Ambae Island 36 Artillery barrages 36 seafloors 36 azure ocean 36 dragonflies buzzing 36 Mandatory Evacuations 36 Cartoon Protests 36 Explosive Found 36 Giant sunbeams burst 36 spewed radiation 36 Iceland Eyjafjallajokull pronounced 36 mortar shells rained 36 Flood Advisories 36 meteor streaked across 36 accretion disks 36 Shiite Stronghold 36 Celebratory gunfire 36 volcanic ash emanating 36 EXPLOSION IN 36 dank odor 36 decaying algae 36 thick grayish haze 36 Substance Found 36 sulfurous gases 36 thunderheads 36 Sectarian Clashes 36 Tel Hawwa 36 Oozes 36 Artillery duels 36 volcanic craters