Editing Yellowstone Caldera (section)

==Eruption history==
A total of {{convert|6500|km3|mi3|abbr=on}} of rhyolite and {{convert|250|km3|mi3|abbr=on}} of basalt were emplaced over three volcanic cycles between about 2.15&nbsp;million and 0.07&nbsp;million years ago.{{sfn|Christiansen|2001|p=69}} Each cycle lasted roughly three-quarters of a million years. The sequence of events in each cycle is similar: a catastrophic rhyolitic ash-flow sheet and caldera collapse, preceded and followed by eruptions of rhyolitic lavas and tuffs and basaltic eruptions near the caldera margin.{{sfn|Christiansen|2001|p=1}} Ash-flow sheets account for more than half of the total volcanic volume of the Yellowstone Plateau.{{sfn|Christiansen|2001|p=68}}

=== First-cycle ===
[[File:Map Volcanic Ashes Yellwostone Eruptions color.png|thumb|Map of the known ash-fall boundaries for major Pleistocene eruptions in Southwest US. By Volcano Hazards Program]]
The first-cycle lasted from about 2.15&nbsp;million to 1.95&nbsp;million years ago, spanning approximately 200&nbsp;kyr.{{sfn|Rivera|Darata|Lippert|Jicha|2017|p=384}} The only known pre-collapse rhyolitic unit is the Rhyolite of Snake River Butte, located just north of [[Ashton, Idaho|Ashton]] and dated at {{Value|2.1398|0.0035|u=million years}},{{sfn|Rivera|Darata|Lippert|Jicha|2017|p=380}} roughly 60–70&nbsp;kyr before the caldera-forming [[Huckleberry Ridge Tuff]].{{sfn|Wotzlaw|Bindeman|Stern|D’Abzac|2015|p=4}} Its vent lies near the eventual first-cycle caldera margin close to the Big Bend Bridge.{{sfn|Christiansen|2001|p=53}} Additional rhyolite flows may have erupted along the incipient ring-fault,{{sfn|Christiansen|2001|p=53}} but the pre-collapse rhyolite history likely spans no more than ~70&nbsp;kyr.{{sfn|Wotzlaw|Bindeman|Stern|D’Abzac|2015|p=4}} Another pre-collapse unit is the {{convert|60|to|70|m|ft|abbr=on}}-thick Junction Butte Basalt on the northeastern margin of the plateau,{{sfn|Christiansen|2001|p=53}} dated at {{Value|2.16|0.04|u=million years}}.{{sfn|Christiansen|2001|p=22}} The [[Overhanging Cliff]] basalt is a flow of this unit.{{sfn|Christiansen|2001|p=53}}

The first-cycle caldera-forming event was the eruption of the [[Huckleberry Ridge Tuff]] at {{Value|2.0773|0.0034|u=million years}} ago, during transitional magnetic polarity.{{sfn|Singer|Jicha|Condon|Macho|2014|p=35}} Its thickness exceeds {{convert|1|km|mi|abbr=on}} in the Red Mountains area.{{sfn|Wilson|2017|p=45}} The initial Plinian phase deposited up to {{convert|2.5|m|ft|abbr=on}} of fallout ash at [[Mount Everts]] before transitioning to ash-flow tuff.{{sfn|Christiansen|2001|p=55}}{{sfn|Wilson|2009}} Early Plinian activity was intermittent, sourced from multiple vents, probably lasted a few weeks and evacuated about {{convert|50|km3|mi3|abbr=on}} of magma from four magma bodies,{{sfn|Swallow|Wilson|Myers|Wallace|2018|p=32}} triggering caldera collapse at the onset of transition to ash-flow.{{sfn|Swallow|Wilson|Charlier|Gamble|2019|p=1374}}{{sfn|Swallow|Wilson|Myers|Wallace|2018|p=32}}
The ash-flow tuff is a composite sheet consisted of three intermittent members, with a total magma volume of about {{convert|2450|km3|mi3|abbr=on}}.{{sfn|Christiansen|2001|p=55}} Member A likely vented from the plateau's central area{{sfn|Christiansen|2001|p=55}} and tapped nine magma bodies.{{sfn|Swallow|Wilson|Myers|Wallace|2018|p=32}} After a hiatus of a few weeks or more,{{sfn|Swallow|Wilson|Charlier|Gamble|2019|p=1374}} the most voluminous Member B erupted from north of Big Bend Ridge.{{sfn|Christiansen|2001|p=57}} After another extended break of years to decades,{{sfn|Swallow|Wilson|Charlier|Gamble|2019|p=1374}} part of the Member A magmatic system was rejuvenated to feed Member C.{{sfn|Swallow|Wilson|Charlier|Gamble|2019|p=1374}} The least voluminous Member C might have source area near the Red Mountains, where it is about {{convert|430|m|ft|abbr=on}} thick.{{sfn|Christiansen|2001|p=59}} Some outcrops of Member A and Member C have been misidentified as Member B, complicating volume estimates of individual ash-flow unit.{{sfn|Phillips|Garwood|Feeney|2014}} Glen&nbsp;A. Izett estimated that an additional {{convert|2000|km3|mi3|abbr=on}} of ash was dispersed as fallout across North America.{{sfn|Izett|1981|p=10201}} Tephra fallout from this event is known as the Huckleberry Ridge ash bed (formerly "Pearlette type&nbsp;B"). Its area covered exceeds {{convert|3400000|km2|sqmi|abbr=on}}.{{sfn|Sarna-Wojcicki|Knott|Westgate|Budahn|2023|p=24}}. It is widely distributed and has been identified in the [[Pacific Ocean]] at [[Deep Sea Drilling Project]] Site&nbsp;36, about {{convert|1600|km|mi|abbr=on}} from Island Park Caldera,{{sfn|Sarna-Wojcicki|Morrison|Meyer|Hillhouse|1987|p=215}} as well as in the [[Humboldt County, California|Humboldt]] and [[Ventura County, California|Ventura]] basins of coastal California,{{sfn|Sarna-Wojcicki|Morrison|Meyer|Hillhouse|1987|p=207}} near [[Afton, Iowa|Afton]] in [[Iowa]], [[Benson, Arizona|Benson]] in [[Arizona]], and Campo Grande Mountain in [[Texas]].{{sfn|Izett|Wilcox|1982}}

One lava flow near the Sheridan Reservoir{{sfn|Watts|Bindeman|Schmitt|2011|p=862}} and two flows at the north end of Big Bend Ridge{{sfn|Christiansen|2001|p=64}} are post-collapse rhyolites of the first-cycle volcanism. The Sheridan Reservoir Rhyolite, dated at {{Value|2.07|0.19|u=million years}},{{sfn|Watts|Bindeman|Schmitt|2011|p=862}} if vented from the Island Park ring-fracture, required a flow distance of at least {{convert|20|km|mi|abbr=on}}.{{sfn|Watts|Bindeman|Schmitt|2011|p=863}} Its volume is estimated to exceed {{convert|10|km3|mi3|abbr=on}}.{{sfn|Watts|Bindeman|Schmitt|2011|p=860}} The other two flows, the Blue Creek flow and the overlying Headquarters flow, have a combined volume of {{convert|10-20|km3|mi3|abbr=on}}{{sfn|Balsley|Gregory|1998|p=130}} and erupted respectively at {{Value|1.9811|0.0035|u=million years}} and {{Value|1.9476|0.0037|u=million years}} ago.{{sfn|Rivera|Darata|Lippert|Jicha|2017|p=380}}

=== Second-cycle ===
After ~500&nbsp;kyr of quiescence,{{sfn|Rivera|Furlong|Vincent|Gardiner|2018|p=236}} a new magmatic system formed north of Big Bend Ridge. It erupted the Bishop Mountain Flow at {{Value|1.4578|0.0016|u=million years}} and the Tuff of Lyle Spring at {{Value|1.4502|0.0027|u=million years}}.{{sfn|Rivera|Furlong|Vincent|Gardiner|2018|p=229}} The Bishop Mountain Flow is a rhyolite with an exposed volume of about {{convert|23|km3|mi3|abbr=on}} and reaches a thickness of {{convert|375|m|ft|abbr=on}} along the inner caldera wall. The Tuff of Lyle Spring is a {{convert|1|km3|mi3|abbr=on}}, composite ash-flow sheet consisting of two cooling units.{{sfn|Rivera|Furlong|Vincent|Gardiner|2018|p=226}} Both eruptions appear to have originated from an isolated, highly evolved local magma chamber distinct from the second-cycle magma source.{{sfn|Christiansen|2001|p=64}} Tiffany&nbsp;A. Rivera et&nbsp;al. (2017) suggest these two eruptions should not be assigned to the second cycle but instead represent the separate Lyle Spring magmatic system.{{sfn|Rivera|Furlong|Vincent|Gardiner|2018|p=236}}
The next pre-collapse rhyolite eruption is the Green Canyon Flow in the north of Big Bend Ridge, with a mapped volume of about {{convert|5|km3|mi3|abbr=on}}, dated at {{Value|1.2989|0.0009|u=million years}}.{{sfn|Rivera|Furlong|Vincent|Gardiner|2018|p=229}} Its age is indistinguishable from that of the subsequent [[Mesa Falls Tuff]], but the Henry's Fork Caldera fracture truncates the Green Canyon Flow, indicating it predates the second-cycle caldera.{{sfn|Rivera|Furlong|Vincent|Gardiner|2018|p=234}}

The second-cycle caldera-forming eruption was the Mesa Falls Tuff, dated at {{Value|1.3001|0.0006|u=million years}}.{{sfn|Rivera|Schmitz|Jicha|Crowley|2016|p=7}} Its exposed thickness exceeds {{convert|150|m|ft|abbr=on}} on Thurmon Ridge, though it is likely much thicker within the caldera.{{sfn|Christiansen|2001|p=64}} During the initial Plinian phase, about {{convert|5|m|ft|abbr=on}} of ash and [[pumice]] were deposited around the [[Ashton, Idaho|Ashton]] area, while much of the vitric ash dispersed to more distant regions, as inferred from the high crystal content of the local deposit. This airfall is overlain by a {{convert|1|m|ft|abbr=on}} [[pyroclastic surge]] layer also enriched in crystals.{{sfn|Neace|1986|p=73}} A single cooling unit of ash-flow tuff followed, covering about {{convert|2700|km2|sqmi|abbr=on}} with an estimated volume of {{convert|280|km3|mi3|abbr=on}}.{{sfn|Christiansen|2001|p=64}} The Mesa Falls ash bed (formerly "Pearlette type&nbsp;S") is the distal ash-fall of this eruption, found in [[Brainard, Nebraska|Brainard]] and [[Hartington, Nebraska|Hartington]] in [[Nebraska]], and in the southern [[Rocky Mountains]] of [[Colorado]].{{sfn|Izett|Wilcox|1982}}

Post-collapse eruptions included the Moonshine Mountain dome{{sfn|Rivera|Furlong|Vincent|Gardiner|2018|p=235}} and five rhyolite domes collectively known as the Island Park Rhyolite.{{sfn|Christiansen|2001|p=66}} The Moonshine Mountain dome, with an estimated volume of {{convert|2.5|km3|mi3|abbr=on}}, erupted at {{Value|1.3017|0.0019|u=million years}}.{{sfn|Rivera|Furlong|Vincent|Gardiner|2018|p=229}} While its age is indistinguishable from the [[Mesa Falls Tuff]], field evidence indicates it formed after the collapse of the [[Henry's Fork Caldera]].{{sfn|Rivera|Furlong|Vincent|Gardiner|2018|p=235}} The dome's magma source is likely the same region that supplied the Bishop Mountain Flow.{{sfn|Stelten|Champion|Kuntz|2018|p=59}}
The Island Park Rhyolite comprises five bodies: Silver Lake dome, Osborne Butte dome, Elk Butte dome, Lookout Butte dome, and Warm River Butte dome.{{sfn|Christiansen|2001|p=66}} These domes collectively have a total volume of {{convert|1-2|km3|mi3|abbr=on}}.{{sfn|Balsley|Gregory|1998|p=130}} All five erupted within a few centuries, around {{Value|1.2905|0.0020|u=million years}}, during a single eruptive episode.{{sfn|Stelten|Champion|Kuntz|2018|p=55}} While Lookout Butte is located on the rim of Big Bend Ridge caldera wall, the vents for the other four domes align along a northwest-trending, structurally controlled linear vent zone about {{convert|30|km|mi|abbr=on}} long and no more than {{convert|7|km|mi|abbr=on}} wide.{{sfn|Christiansen|2001|p=67}}

=== Third-cycle ===
Pre-collapse third-cycle silicic rocks are broadly divided into the [[Mount Jackson (Wyoming)|Mount Jackson]] Rhyolite and the [[Lewis River (Wyoming)|Lewis Canyon]] Rhyolite,{{sfn|Christiansen|2001|p=17}} which vented along what later became the ring-fracture zone of the third-cycle caldera.{{sfn|Christiansen|2001|p=19}}
The earliest known lava in this cycle is the Wapiti Lake flow of the Mount Jackson group, dated at {{Value|1.2187|0.0158|u=million years}},{{sfn|Troch|Ellis|Mark|Bindeman|2017|p=7}} exposed near the [[Grand Canyon of the Yellowstone]] and likely vented near Wapiti Lake.{{sfn|Christiansen|2001|p=24}} Another flow, the Moose Creek Butte flow ({{Value|1.1462|0.0022|u=million years}}), also belongs to the Mount Jackson group.{{sfn|Stelten|Champion|Kuntz|2018|p=53}} Although younger than the Island Park Rhyolite, its geochemical similarity has led some researchers to propose it as a second-cycle post-collapse eruption.{{sfn|Troch|Ellis|Mark|Bindeman|2017|p=14}} [[Pumice]] of an unknown tuff unit at Broad Creek has an age range from {{Value|0.948|0.016|u=million years}} to {{Value|1.11|0.02|u=million years}}.{{sfn|Obradovich|1992|p=10}}
Later Mount Jackson eruptions include the Flat Mountain Rhyolite ({{Value|0.929|0.034|u=million years}}){{sfn|Christiansen|2001|p=21}} and the Harlequin Lake flow ({{Value|0.8300|0.0072|u=million years}}).{{sfn|Troch|Ellis|Mark|Bindeman|2017|p=7}} The Lewis Canyon Rhyolite group contains lavas dated to {{Value|0.8263|0.0184|u=million years}},{{sfn|Troch|Ellis|Mark|Bindeman|2017|p=7}} though Robert L. Christiansen suggests they could be late-stage first-cycle eruptions.{{sfn|Christiansen|2001|p=25}}
A recently discovered ash-flow unit is dated to {{Value|0.796|u=million years}}.{{sfn|Myers|Henderson|Salazar|Wilson|2024}} An explosive eruption deposited pumiceous fallout near Harlequin Lake,{{sfn|Christiansen|2001|p=17}} which is immediately overlain by the Mount Haynes lava ({{Value|0.7016|0.0014|u=million years}}).{{sfn|Troch|Ellis|Mark|Bindeman|2017|p=7}} An ash bed from a Yellowstone eruption was deposited in the [[Great Salt Lake]] approximately {{Value|0.7|u=million years}} ago.{{sfn|Perkins|Nash|2002|p=374}}
The age of the Big Bear Lake flow is uncertain, but it lies beneath the third-cycle caldera-forming [[Lava Creek Tuff]].{{sfn|Christiansen|2001|p=17}} Additional Mount Jackson flows may be buried within the Yellowstone caldera, inferred from intracaldera topography.{{sfn|Christiansen|2001|p=25}}

The climatic ash-flow eruption of the third cycle was the Lava Creek Tuff, dated at {{Value|0.6260|0.0026|u=million years}},{{sfn|Wotzlaw|Bindeman|Stern|D’Abzac|2015|p=4}} during a glacial–interglacial transition in the [[Marine isotope stages|Marine Isotope Stage]].{{sfn|Matthews|Vazquez|Calvert|2015|p=2524}} This composite tuff sheet consists of at least two members, distinguishable by a widely occurring welding intensity decrease between them,{{sfn|Christiansen|2001|p=26}} and represents a total ash-flow volume of about {{convert|1000|km3|mi3|abbr=on}}.{{sfn|Christiansen|2001|p=31}}
Member A likely erupted south of [[Purple Mountain (Wyoming)|Purple Mountain]], where it reaches its greatest thickness of {{convert|430|m|ft|abbr=on}} and exhibits maximum welding.{{sfn|Christiansen|2001|p=31}} The Purple Mountain to Gibbon Canyon segment of caldera wall collapsed after the emplacement of Member A but before it completely cooled.{{sfn|Christiansen|2001|p=38}} A {{convert|20-30|cm|in|abbr=on}} loose crystal ash unit separates Member A from Member B, indicating a break in the eruption sufficiently long for cooling of thick ash-flows.{{sfn|Christiansen|2001|p=29}} A {{convert|3|m|ft|abbr=on}} thick pumiceous ash-fall deposit underlies Member B and probably marks its initial phase.{{sfn|Christiansen|2001|p=29}} Member B ash-flows extends radially outward along paleovalleys and more extensive plateau segments. The eruptive center for Member B appears to be situated farther east compared to that of Member A.{{sfn|Christiansen|2001|p=34}} However, this simplistic eruptive sequence has been challenged.{{sfn|Wilson|Stelten|Lowenstern|2018|p=52}} An additional {{convert|40|m|ft|abbr=on}} ash-flow unit (informally named unit 2) has been identified, venting from around Bog Creek. Unit 2 erupted some decades after Member A had cooled{{sfn|U.S. Geological Survey|2024|p=29}} and overlies tuff fragments from Member A.{{sfn|Myers|Henderson|Salazar|Wilson|2024}} Two additional rhyolite ash-flow units (unit 3 and unit 4) have been recognized, erupting from a vent near Stonetop Mountain and are previously undocumented parts of the Lava Creek Tuff.{{sfn|U.S. Geological Survey, Volcano Science Center|2024|p=29}} An unknown welded tuff underlying Member B at Flagg Ranch, not attributed to Member A, was emplaced shortly before the initial ashfall of Member B and is considered part of the early Lava Creek eruption.{{sfn|Henderson|2023}} Rather than having the simple structure of just two ignimbrite sheets, the Lava Creek Tuff may consist of multiple ash-flow lobes from distinct magma bodies.{{sfn|Myers|Henderson|Salazar|Wilson|2024}} The ash fallout from the Lava Creek Tuff eruption is known as the Lava Creek ash bed (formerly "Pearlette type&nbsp;O"),{{sfn|Izett|Wilcox|1982}} covering an area exceeding {{convert|3000000-4000000|km2|sqmi|abbr=on}}.{{sfn|Sarna-Wojcicki|Knott|Westgate|Budahn|2023|p=24}} Perkins and Nash (2002) estimated that the volume of this ash bed is greater than {{convert|500|km3|mi3|abbr=on}}.{{sfn|Perkins|Nash|2002|p=377}} It has been identified in the [[Gulf of Mexico]],{{sfn|Sarna-Wojcicki|Davis|1991|p=112}} near [[Regina, Saskatchewan]],{{sfn|Westgate|Christiansen|Boellstorff|1977|p=357}} in [[Ventura, California]],{{sfn|Sarna-Wojcicki|Morrison|Meyer|Hillhouse|1987|p=216}} and in [[Viola Center, Iowa]].{{sfn|Izett|Wilcox|1982}}

==== Post-collapse rhyolites ====
Post-collapse rhyolites likely erupted shortly after the Lava Creek Tuff.{{sfn|Christiansen|Lowenstern|Smith|Heasler|2007|p=7}} The subaerial post-collapse silicic rocks are collectively referred to as the Plateau Rhyolite,{{sfn|Christiansen|2001|p=39}} which primarily consists of lava flows.{{sfn|Christiansen|Lowenstern|Smith|Heasler|2007|p=7}} Plateau Rhyolite is divided into three intracaldera members—Upper Basin Member, Mallard Lake Member, and Central Plateau Member—and two extracaldera members—Obsidian Creek Member and Roaring Mountain Member.{{sfn|Christiansen|2001|p=40}} It is likely that rhyolitic pumice and ash were erupted during the opening of vents for each of these lava flows.{{sfn|Christiansen|Lowenstern|Smith|Heasler|2007|p=7}}
The earliest intracaldera rhyolite, the East Biscuit Basin Flow of the Upper Basin Member, is dated to {{Value|0.635|0.014|u=million years}}, followed by [[felsic]] lithic clasts of an unknown unit ({{Value|0.6|0.02|u=million years}}) in [[Yellowstone Lake]],{{sfn|Morgan|Shanks|2005|p=37}} and the North Biscuit Basin Flow ({{Value|0.580|0.040|u=million years}}).{{sfn|Till|Vazquez|Stelten|Shamloo|2019|p=3868}} The earliest extracaldera rhyolite is the Riverside Flow ({{Value|0.5258|0.0033|u=million years}}) of the Roaring Mountain Member,{{sfn|Nastanski|2005|p=47}} broadly contemporaneous with the Middle Biscuit Basin Flow ({{Value|0.527|0.028|u=million years}}).{{sfn|Till|Vazquez|Stelten|Shamloo|2019|p=3868}} Two ash-flow tuff units of the Upper Basin Member include the {{convert|35|m|ft|abbr=on}}-thick Tuff of Uncle Tom’s Trail{{sfn|Christiansen|2001|p=40}} and the {{convert|230|m|ft|abbr=on}}-thick Tuff of Sulphur Creek{{sfn|Pritchard|Larson|2012|p=209}}, the latter dated at {{Value|0.479|0.02|u=million years}}.{{sfn|Christiansen|2001|p=27}} Tuff of Sulphur Creek is at least {{convert|13|km3|mi3|abbr=on}}.{{sfn|Manley|McIntosh|2002|p=220}} These tuffs were deposited on the north flank of the Sour Creek dome.{{sfn|Christiansen|2001|p=40}} The Canyon lava flows of the Upper Basin Member erupted immediately after the Tuff of Sulphur Creek, as the ash-flow was still hot at the time of emplacement.{{sfn|Christiansen|2001|p=42}} Both the Tuff of Sulphur Creek and Canyon flows originated from a vent near Fern Lake.{{sfn|Christiansen|2001|p=42}} The two tuffs and Canyon flows have a combined magma volume of {{convert|40-70|km3|mi3|abbr=on}}.{{sfn|Balsley|Gregory|1998|p=130}}
The Dunraven Road Flow ({{Value|0.486|0.042|u=million years}}) of the Upper Basin Member overlies the Canyon flows{{sfn|Christiansen|2001|p=42}} and may have had an extracaldera vent.{{sfn|Pritchard|Larson|2012|p=226}} The Cougar Creek lava dome of the Roaring Mountain Member erupted {{Value|0.358|0.002|u=million years}} north of the caldera.{{sfn|Christiansen|Lowenstern|Smith|Heasler|2007|p=78}}
Four additional lava flows of the Obsidian Creek Member—Willow Park dome, Apollinaris Spring dome, Gardner River complex, and Grizzly Lake complex—erupted between {{Value|0.326|0.002|u=million years}} and {{Value|0.263|0.003|u=million years}},{{sfn|Christiansen|Lowenstern|Smith|Heasler|2007|p=78}} in the vicinity of [[Norris Geyser Basin]] northward toward [[Mammoth Hot Springs]].{{sfn|Christiansen|2001|p=48}} The South Biscuit Basin Flow of the Upper Basin Member erupted {{Value|0.257|0.009|u=million years}} ago.{{sfn|Till|Vazquez|Stelten|Shamloo|2019|p=3868}} The Scaup Lake Flow of the Upper Basin Member is dated to {{Value|0.244|0.009|u=million years}},{{sfn|Till|Vazquez|Stelten|Shamloo|2019|p=3868}} while the Landmark dome of the Obsidian Creek Member is {{Value|0.226|0.006|u=million years}}.{{sfn|Christiansen|Lowenstern|Smith|Heasler|2007|p=78}}

Non-explosive eruptions of [[lava]] and less-violent explosive eruptions have occurred in and near the Yellowstone caldera since the last supereruption.<ref>{{cite journal |last1=Bindeman |first1=Ilya N. |last2=Fu |first2=Bin |last3=Kita |first3=Noriko T. |last4=Valley |first4=John W. |title=Origin and Evolution of Silicic Magmatism at Yellowstone Based on Ion Microprobe Analysis of Isotopically Zoned Zircons |journal=Journal of Petrology |date=January 2008 |volume=49 |issue=1 |pages=163–193 |doi=10.1093/petrology/egm075|doi-access=free |citeseerx=10.1.1.583.1851 }}</ref><ref>{{cite web|title=Secrets of supervolcanoes|url=http://pages.uoregon.edu/bindeman/Supervolcanoes.pdf|publisher=University of Oregon}}</ref> The most recent lava flow occurred about 70,000 years ago, while a violent eruption excavated the West Thumb of Lake Yellowstone 174,000 years ago. Smaller [[steam explosion]]s occur as well. An explosion 13,800 years ago left a {{convert|5|km|abbr=on}} diameter [[volcanic crater|crater]] at Mary Bay on the edge of Yellowstone Lake (located in the center of the caldera).<ref>{{cite web| title = Introduction to hydrothermal (steam) explosions in Yellowstone| work = Yellowstone National Park| publisher = Yellowstone Net| url = http://www.yellowstone.net/hydrothermal.htm| access-date = December 31, 2008| archive-date = January 6, 2009| archive-url = https://web.archive.org/web/20090106140637/http://www.yellowstone.net/hydrothermal.htm| url-status = dead}}</ref> Currently, volcanic activity is exhibited via numerous [[geothermal areas of Yellowstone|geothermal vents]] scattered throughout the region, including the famous [[Old Faithful Geyser]], plus recorded ground-swelling indicating ongoing inflation of the underlying magma chamber.{{Citation needed|date=September 2021}}