Mount Trident erupted intermittently from 1953-1974. Some (Miller and others, 1998) consider this period as one eruptive event while others (Simkin and Siebert, 1994) break it up into discrete, separate eruptions. Detailed timelines and observations of the eruptive activity at Mt. Trident during this time can be found in Decker, 1963; Ray, 1967, and Ward and Matumoto, 1967. Synder (1954) gives extremely detailed information about events in 1953 and 1954.
Hildreth and others (2003) summarize the eruption as follows: "Beginning in February 1953, a new andesite-dacite edifice (0.7-cubic km volume) was built at the southwestern margin of the Trident group [see unit tsw, fig. 3, in original text]. Though sometimes referred to informally as 'New Trident,' we have called it Southwest Trident (Hildreth and others, 2000), in anticipation of the day it ceases to be Trident's youngest component. During 2 decades of sporadic explosive activity (Vulcanian type and effusive), a new composite cone covering about 3-square km area was constructed of block-and-ash deposits, scoria, agglutinate, stubby lava lobes, and the intercalated proximal parts of the main lava flows that spread as an apron beyond the cone. The cone grew to an elevation of 4,970 ft (1,515 m) (Global Positioning System measurement by Coombs and others, 2000) on the former site of a 100-m-wide fumarolic pit at about 3,840-ft (1,170 m) elevation on the steep southwest flank of Trident I. Although relief on its south slope exceeds 700 m [see fig. 13 in original text], the new cone thus has a central thickness of only 345 m and a volume of about 0.3 cubic km. At successive stages of cone construction, four blocky leveed lava flows effused from its central vent, in 1953, 1957, and 1958 and during the winter of 1959-60 [see figs. 3, 13 in original text]. Each flow is 25 to 60 m thick and 2.5 to 4 km long, and altogether they add about 0.35 cubic km to the eruptive volume. The cone's summit is today marked by a shallow crater, 350 m wide [see fig. 14 in original text], that was the site of several small ephemeral plugs, which were emplaced after the final lava flow and were repeatedly destroyed by intermittent explosive activity (1960-74).
"Black, rapidly expanding, cauliflower ash clouds rose 6 to 9 km at least 10 times between 1953 and 1974 and possibly 12 km once or twice. Several times during the first month of activity, light ashfall dusted areas as far as 30 to 50 km from the vent, in all sectors. By far the most voluminous fallout appears to have resulted from the initial outburst of February 15, 1953 (Snyder, 1954), which may have been sub-Plinian. A single nongraded scoria-fall layer (5-17 cm thick) deposited during that event is preserved at a few protected sites as far away as Mount Katmai and upper Knife Creek. Sieve data for bulk samples of this layer yield median and maximum particle sizes, respectively, of 6.5 and 100 mm in the saddle 1 km north of the vent, and 2.1 and 20 mm in the saddle 7 km northeast of the vent - between the twin western summits of Mount Katmai. Thin sheets of finer ash that fell during the many smaller subsequent outbursts have been almost entirely removed or reworked by wind and runoff. Abundant ballistic blocks, variously breadcrusted, densely vitrophyric, or scoriaceous, that are scattered as far as 3 km from vent are products of many discrete explosive episodes (none of which were closely observed) distributed over 2 decades. Liberal estimates of total fallout volume yield no more than 0.05 cubic km, contributing less than 10 percent of the total eruptive volume of 0.7+/-0.1 cubic km.
"The period of most frequent observation was from February to September 1953, principally by military reconnaissance aircraft during the early months (Snyder, 1954) and by a U.S. Geological Survey (USGS) party that camped at Knife Creek during the summer (Muller and others, 1954). When the vent was first seen through the cloud layer on the fourth day of activity (Feb. 18, 1953), an effusive lava flow (then already 250 m wide) was upwelling centrally and spreading radially (fig. 15A). Although a fumarolic pit, as much as 40 m deep, was conspicuous at the impending ventsite on aerial photographs taken in 1951 (and had probably been further excavated by the explosive outburst of Feb. 15), any such crater was soon filled and buried by the effusive lava [see fig. 15A in original text], which continued to be extruded and spread slowly throughout the seven months of intermittent observation in 1953. At various times, lava lobes emerged laterally through the chilled carapace at the foot of the pile, or the pile itself 'expanded like a balloon' and extruded lobes by overflow from the vent, or small slumps and slide masses detached from the steep flow margins (Snyder, 1954). By June 1953, the main southerly tongue of lava, ultimately 4.2 km long, had advanced only 1,250 m from the vent. Snyder (1954) estimated the volume of fallout and lava produced by June 17, 1953, at 0.23 to 0.3 cubic km, about a third of the eventual output. During the summer, steady steaming and continued spreading of the lava was punctuated sporadically by steam bursts [see fig. 15B in original text] or occasional 'smoke columns' that rose 1 to 3 km and dusted various proximal sectors with minor additional ashfall (Muller and others, 1954).
"Observations after September 1953 were sporadic and few. A general chronology of major events was compiled by Decker (1963) and augmented by Ray (1967), largely from intermittent National Park Service reports. The 1953 lava flow may not have attained its final dimensions [see fig. 3 in original text] until early 1954 or later. Apparently, no observations were made during eruption and outflow of the lava flows of 1957, 1958, and 1959-60 [see fig. 3 in original text], merely aerial snapshots taken in the summer seasons after the emplacement of each flow. The time of emplacement of the lava flow attributed to the winter of 1959-60 is the least well known, because no photographs are known to have been taken between September 1958 and August 1960. The 1958 lava flow partly overran the 1953 flow [see fig. 3 in original text] and impounded a small lake on upper Mageik Creek that soon filled in with pumiceous alluvium, becoming a mudflat (Ferruginous Flat) now marked by numerous iron-precipitating warm springs.
"Growth of the fragmental cone [see figs. 13, 14 in original text] began only after much or all of the 1953 lava flow [see fig. 15 in original text] had been emplaced. The cone accumulated progressively during the later 1950s, as shown by emergence of the successive lava flows at different levels of the fragmental edifice. National Park Service photographs show that the cone had attained nearly its full height by 1960, although explosive showers of blocks continued to augment the cone until 1974. In addition to the four main lava flows, cone construction included emplacement of several stubby lava lobes limited to its proximal southwest slope [see fig. 3 in original text]. The southeast side of the cone completely buried a 1-km-square-area cirque glacier, with no recognized effects on eruptive behavior or edifice structure, although enhanced steaming may have contributed to the stronger fumarolic emission and alteration on that side of the cone [see fig. 14 in original text]. Explosive ejections of tephra, some involving blowout of plugs and at least one spine, took place from 1960 to 1974, but volumetrically significant eruptions were over by 1963. Numerous sulfurous fumaroles, superheated in the 1960s but below and at the boiling point today, persist on the upper parts of the cone [see fig. 14 in original text]. Dark-gray bouldery debris flows reworked from the pyroclastic deposits have built a proximal fan and thin distal sheets (1-4 m thick) that cap stream terraces for 3 km downstream along Mageik Creek. Some debris flows resulted from the initial February 1953 fallout over snow, and others from avalanching of rubble from the steep slopes of the cone."

On August 24, 2022, an earthquake swarm began beneath Trident volcano in the Katmai area. The first earthquakes were at deep levels in the crust, around 16 miles below sea level, but progressed upward to about 3 miles beneath the surface over the next five days. Dozens of magnitude 0.7 to 1.9 earthquakes happened each day over this time period, but the rate of earthquakes dropped off somewhat after the 28th. There were also a few periods of volcanic tremor and low-frequency earthquakes.
On September 14, 2022, AVO released an Information Statement about the earthquake activity at Trident, stating that no other signs of unrest had been observed and that the seismic activity was likely caused by movement of magma or magmatic fluids.
After the earthquakes continued into the next month, AVO raised the alert levels to YELLOW/ADVISORY on September 29.
On October 19, 2022, citing that the rate of earthquakes had dropped and seismic tremor had not observed since September 30, 2022, AVO lowered the Aviation Color Code to GREEN and the Volcano Alert Level to NORMAL.
On November 20, there was a magnitude 4.6 quake – this was far larger than most of the quakes in the area.
In late 2022 into January 2023, the rate of earthquakes began to pick up again. There were also more earthquakes occurring under Mount Katmai to the east, and under Martin and Mageik volcanoes to the west, though the largest number of earthquakes continued to be beneath Trident, as well as periods of tremor.
On January 11, 2023, AVO released an information statement for Katmai, Trident, Martin, and Mageik volcanoes, noting this more elevated activity.
On February 22, 2023, AVO again raised the Aviation Color Code and Volcano Alert Level at Trident to YELLOW/WATCH, stating that earthquakes were continuing to occurr at about 10 per day. The notice also stated that because of the tremor observed beneath Trident and the initial swarm there, the unrest in the broader Katmai region was likely, though not certain, because of magma or magmatic fluid movement beneath Trident.
In May 2023, AVO began detecting a marked increase in low-frequency earthquakes—in addition to regular earthquakes—at shallow and deep levels in the region between Trident and Novarupta, which lies 3 miles to the northwest. These types of earthquakes often indicate the movement of magma or magmatic fluids within the Earth’s crust. The deep low-frequency earthquakes were often accompanied by longer-duration bursts of continuous tremor, indicating deep fluid movement.
In June, satellite radar data taken in newly snow-free conditions was compared to data taken in the fall, which showed that Trident Volcano had inflated slightly, with the ground uplifted by about 2 inches, especially on the southern flank.
On July 25, 2023, AVO released another Information Statement about this activity, noting that earthquakes also continued to occur around Mount Katmai and Martin and Mageik volcanoes, but AVO continued to believe this was likely a secondary effect of magma/magmatic fluid intrusion beneath Trident.
After July, earthquake activity remained elevated, and deep low-frequency earthquakes and periods of tremor continued. In September AVO noted that there was an increase in the rate of earthquakes very deep in the crust (greater than 9 miles down), as well as some minor additional ground deformation.
Beginning in early October rates of earthquake activity declined somewhat, especially deeper earthquakes. AVO noted that this might indicate a decline in magma/magmatic fluid activity beneath Trident.
Seismicity remained slightly elevated in December.
In the first week of January, AVO noted that while earthquakes were still occurring, their rate was now approaching the typical or "background" state for the Katmai area. Due to this, AVO lowered the alert levels back to GREEN/NORMAL on January 10, 2024.