1971 Formula One season

Austrian Jochen Rindt was accorded the championship posthumously in 1970 for Lotus-Ford; he was killed at Monza during practice for the Italian Grand Prix in September of that year. His enormous points lead after 4 consecutive championship Grand Prix victories in 1970 effectively consolidated his championship status that year. Briton Jackie Stewart, world champion in 1969, had a transitional year in 1970, using a customer March car after Matra refused to allow Stewart's boss Ken Tyrrell to put a Ford-Cosworth DFV V8 in their car in place of Matra's own V12. Tyrrell was designing his own car in secret in England, and the March was an interim solution. The new Tyrrell 001 car was first raced by the Scottish Stewart at the Mont-Tremblant circuit in Quebec, Canada- and was immediately competitive, but he retired due to mechanical failure. The car's competitiveness enabled designer Derek Gardner to produce an even more competitive car for the 1971 season- the Tyrrell 002 and 003. 002 had a longer wheelbase and was exclusively for Stewart's tall French teammate Francois Cevert, and 003 was exclusively for the short Stewart. These 2 cars were mechanically almost identical; the only difference being the longer wheelbase for Cevert's height.

Over the winter months Ferrari technical director Mauro Forghieri and his engineers at Ferrari developed the car into 312B/2 form. Jacky Ickx and Clay Regazzoni were retained but the team's third driver, Italian Ignazio Giunti was killed in January during the Buenos Aires 1000 kilometer long-distance sportscar race. Jean-Pierre Beltoise was pushing his Matra sportscar back to the pits when he was hit by Giunti's Ferrari 312P; the Italian was killed in the ensuing crash. As a result, Mario Andretti was hired on a part-time basis to be the team's third driver; Andretti had been driving Ferraris in long distance sportscar races during the two previous years. Tyrrell retained Jackie Stewart and Francois Cevert, while Team Lotus also developed its 1970 car for Brazilian Emerson Fittipaldi and Swede Reine Wisell (although design work was progressing on the Lotus 56, a gas turbine car powered by Pratt & Whitney engines). March lost both of its 1970 drivers: Chris Amon, moving to Matra to join Beltoise and Jo Siffert replacing Jack Oliver at BRM as teammate to Pedro Rodriguez and new driver Howden Ganley. McLaren continued with Denny Hulme and Peter Gethin but the Alfa Romeo engines used by Andrea de Adamich moved to March where the Italian became Ronnie Peterson's teammate in the curious March 711 factory cars. Rob Walker decided that he could no longer afford to continue his private team and transferred his Brooke Bond Oxo sponsorship to Surtees, which recruited second driver Rolf Stommelen (with backing from Auto Moto und Sport and Eifelland caravans) from Brabham.

Walker's decision to stop racing freed veteran Graham Hill and he moved to Brabham (which was now being run by Ron Tauranac, and would be bought by Bernie Ecclestone that year) where he was joined by former Williams driver Tim Schenken while Williams entered old Marches for Derek Bell and Matra refugee Henri Pescarolo.

The first Argentine Grand Prix since 1960 was held as a non-championship Grand Prix in the sweltering heat of a January summer in the capital city of Buenos Aires; the reason for this was that the FIA stipulated that in order for a country to host an official championship Grand Prix round, the organizers had to prove themselves by successfully running an interim non-championship round to their standards. This round, held at the slightly modified Buenos Aires Autodrome (the same venue used before). This race, run in 2 heats was won by New Zealander Chris Amon in a Matra.

The South African Grand Prix, held at the fast and flowing high-altitude Kyalami circuit between Johannesburg and Pretoria in March kicked off the championship season on an interesting note- with raceday traditionally held on a Saturday in South Africa. Stewart took pole, ahead of the twelve cylinder cars of Amon, Regazzoni and Andretti. At the start, Regazzoni made a very good start and took the lead going into the Crowthorne corner ahead of Fittipaldi, Ickx (who had made a lightning start from 8th); Hulme, Rodriguez, Andretti, and Stewart- who had made a bad start. Amon had made a terrible start and had dropped to 14th. Hulme in his McLaren-Ford passed Fittipaldi for second then Regazzoni for the lead. Hulme led the race until the 76th of 79 laps- when he tragically had to come into the pits to repair some suspension damage his car had suffered. Andretti took the lead and won, followed by Stewart, Regazzoni, Wisell, Amon, and Hulme.

There were 3 notable non-championship events between the first and second 1971 Formula One championship rounds. A number of teams traveled to England (where most F1 teams were and are based) to compete in the Race of Champions 2 weeks after the South African Grand Prix, held at the undulating and bumpy Brands Hatch circuit just outside London. This race, run at a shorter distance than is usual for a Grand Prix was won by the Swiss Regazzoni in a Ferrari, ahead of pole-sitter Jackie Stewart and veteran Briton John Surtees.

The Questor Grand Prix in the western United States was held 1 week after the Race of Champions. This race was held at the Ontario Motor Speedway 45 minutes east of Los Angeles in sunny southern California. The Ontario Motor Speedway was an almost exact copy of the world-famous Indianapolis Motor Speedway; although it had what Indianapolis didn't have at the time- an interior road circuit which also utilized part of the speedway oval - and state-of-the-art facilities. This race, like the Argentine race was run in 2 heats; Mario Andretti won this race in a Ferrari ahead of Jackie Stewart - who had finished 2nd for the 3rd F1 race in a row. Financial problems for the organizers meant that Ontario was never to be used again for a Formula One race; Ontario fell into financial disrepair and was closed in 1980. The Auto Club Speedway of California in nearby Fontana effectively replaced this venue in 1996.

Another race in England, the Spring Trophy, this time at the fast, challenging and rather dangerous Oulton Park circuit near England's second largest city, Manchester. This event was not entered by Ferrari, and Stewart took pole again ahead of Briton Peter Gethin in a McLaren-Ford, Rodriguez and Siffert BRMs. In misty, damp and cold weather- typical of English weather in April- rain master Rodriguez won this event, ahead of Gethin and Stewart.

The Spanish Grand Prix in 1971 was held at the spectacularly fast and challenging Montjuic Park city street circuit in Barcelona; the year previous it was held at the tight and twisty Jarama permanent circuit near Madrid in 1970 as part of a rotation with the Catalan circuit. The Ferraris of Ickx and Regazzoni were 1-2 on the grid respectively, followed by Amon, Stewart, Rodriguez, Beltoise, Gethin and Andretti; 6 of the first 8 cars had 12-cylinder engines- a testament to the power needed to do well at Montjuic Park. The race was a rather different matter however, as Stewart made a lightning start to second place at the start, chasing Ickx. On lap six the Scot forced his way into the lead. Behind the leaders, Amon overtook Regazzoni for third place on lap 3, but then the order settled down. Stewart began to increase his lead over Ickx while Amon ran third; Regazzoni went out on lap 13 with a fuel pump failure which promoted Rodriguez to fourth place with Andretti fifth and Denny Hulme sixth in his McLaren-Ford. In the mid-race Andretti disappeared with an engine problem and so Hulme moved to fifth place and Beltoise took sixth. In the closing laps Ickx closed the gap to Stewart but he was still 3.4secs behind at the finish, ahead of Amon.

A third non-championship round took place in England 3 weeks after the Spanish Grand Prix- International Trophy race at the very fast Silverstone airfield circuit 90 minutes north of London. This race also included Chevrolet-powered Formula 5000 cars. Ferrari did not enter, and this race, run in 2 heats was won by British veteran Graham Hill in a Brabham-Ford.

2 weeks after the non-championship International Trophy race and 5 weeks after the second round in Spain came the most prestigious round of the calendar- the Monaco Grand Prix, which was also the 200th World Championship Grand Prix. Qualifying was run in rainy conditions; but Stewart was once again dominant, taking pole by 1.2 seconds from Jacky Ickx's Ferrari. The second row featured Siffert's BRM and Amon's Matra; then it was Rodriguez, Hulme, Beltoise, Ronnie Peterson in a March, Hill and John Surtees in a car of his own construction. Team Lotus were far down with Wisell 11th and Fittipaldi 17th. Amon had problems before the start (Amon got going half a lap behind the field) so Ickx and Stewart were left to fight for the first corner with Siffert, who managed to slip ahead of the Ferrari and take second place behind Stewart. Five time Monaco Grand Prix winner Graham Hill made a mistake on this occasion and crashed on the second lap and his Brabham teammate Tim Schenken hit a barrier two laps later while swerving to avoid Francois Cevert's Tyrrell-Ford when the car's engine cut. Both men got going again but Cevert crashed two laps later when the DFV engine cut again. Stewart gradually increased his lead but the man making the most impact was Peterson who climbed up to second place in the mid-race, passing both Ickx and Siffert. Stewart was able to hold on to take victory ahead of Peterson and Ickx; Siffert later went out with an engine failure and so fourth place went to Hulme.

The Belgian Grand Prix was originally supposed to be held as a championship round 2 weeks after the Monaco event on 6 June at the notoriously dangerous and extremely fast 8.7 mile (14.1 km) Spa-Francorchamps circuit, but the failure of the track owners and authorities to bring Spa up to mandatory safety specs meant that the rural circuit was deemed unsuitable for Formula One cars to race on and the event was promptly cancelled. Formula One did not return to Spa until 1983, when it was re-designed and shortened in 1979.[1]

Another non-championship round, the Rhein-Pokalrennen 3 weeks after the Monaco Grand Prix, was held at the very fast Hockenheim circuit in West Germany, and was won by Jacky Ickx in a Ferrari. This race was run on the same day as the final day of the 24 Hours of Le Mans sportscar race in western France.

One week after the non-championship Hockenheim event and 4 weeks after Monaco was the Dutch Grand Prix, held at the very fast and dangerous beach side Zandvoort circuit half an hour west of Amsterdam- this was an old fashioned circuit which was bumpy and had almost no safety features. Ickx took pole, ahead of Rodriguez, Stewart, Regazzoni and Amon- 4 of the 5 top qualifiers were in 12 cylinder cars. This race was run in wet conditions, and at the start Mario Andretti's Ferrari was missing because of a fuel pump problem. He did start the race but was a long way behind and retired after just a few laps.

Ickx went ahead of Rodriguez, Stewart and Amon. Siffert blew his chances with a spin. On the second lap Amon spun out and on the third lap Stewart had a rare spin and dropped to eighth place; the Goodyear-shod runners were suffering compared to the Firestone-shod cars. This left Regazzoni third and Surtees fourth ahead of Wisell. The Swede did not last long because a rear wheel worked loose and trying to solve the problem he reversed into the pitlane and was disqualified. As everyone else struggled Ickx and Rodriguez built up a big lead with Rodriguez moving ahead on the ninth lap. Their thrilling duel would continue for most of the afternoon but towards the end Ickx pulled away to win by nearly eight seconds. Regazzoni finished third. The Dutch Grand Prix was not held in 1972 due to the outdated facilities of the circuit; it returned for 1973.

2 weeks after the Dutch race was the French Grand Prix at the brand new Paul Ricard circuit near Marseille in the south of France. This circuit, in stark comparison to the rudimentary facilities of Zandvoort was one of the most modern racing circuits in the world; with a smooth surface and state-of-the-art facilities not seen before in Formula One; this was a sign of things to come over the next decades. It also had a long 1.1 mile straight, typical of French circuits. In the 2 previous years, the French Grand Prix was held at the twisty Charade public road circuit near Clermont-Ferrand; this was a very different type of circuit to Paul Ricard. Stewart took pole ahead of Regazzoni, Ickx and surprisingly Graham Hill in a Brabham. At the start Stewart went into the lead with Regazzoni chasing. Ickx was in trouble with his engine and dropped quickly back to retire while there was a battle for third place between Rodriguez and Beltoise. On the 19th lap Peterson's Alfa Romeo engine blew up and Regazzoni spun off on the oil. Hill had a similar accident but was able to get going and pit for repairs. This left Rodriguez in second place. By then, Cevert had moved into third later the ignition in Rodriguez's BRM failed. So Cevert found himself promoted to second place behind Stewart, giving Tyrrell a 1-2 finish. Third place went to Fittipaldi who had driven a good race to come up through the field after starting from 17th.

2 weeks after France was the British Grand Prix at Silverstone. The F1 circus came to this very fast airfield circuit minus one of its top drivers: Pedro Rodriguez had been driving a Ferrari 512S sportscar at a German Interserie race at the Norisring street circuit, and he crashed very badly and was killed. The popular Mexican was 31. At the start Regazzoni and Ickx took the lead for Ferrari with Stewart third. At the tail of the field Oliver ran into the back of Graham Hill's Brabham, putting both men out of the race. Stewart and Siffert overtook Ickx during the second lap and on lap four Stewart overtook Regazzoni at Stowe Corner. The Scottish star immediately began to build up a lead. Siffert overtook Regazzoni in the course of the fifth lap and then things began to settle down with Stewart ahead of Siffert, Regazzoni and Ickx. The major interest in the race was supplied by Fittipaldi, who had made a bad start and was driving through the field from 11th place at the end of the first lap. Siffert began to suffer vibration problems and was caught and repassed by Regazzoni on lap 17. On lap 37 Ickx went into the pits to retire with engine trouble and five laps later Siffert also disappeared with a bad misfire. This put Peterson up to third place with Schenken and Fittipaldi chasing him. On Lap 48 Regazzoni disappeared with engine trouble. Stewart kept going and it looked as though Peterson and Schenken were going to be the other men on the podium but with a few laps to go Schenken suffered transmission failure and retired, leaving third place for Fittipaldi, and a home victory for Stewart, ahead of Peterson. Everyone else was lapped.

The prestigious German Grand Prix was next- and F1 returned to an updated 14.2 mile (22.8 km) Nurburgring after a year's absence from the legendary race track. The drivers had refused to race at this very demanding, twisty, dangerous and difficult circuit in 1970 due to safety issues. However, the entire circuit had been resurfaced and lined with a lot of Armco barrier, some of the worst bumps and jumps were taken out or smoothed over and the circuit was made less twisty, and was therefore a little faster than before. But with the layout being more or less exactly the same as before, the circuit was still dangerous and still the greatest test of a Grand Prix driver's skill- by far. Stewart took pole ahead of Ickx, Siffert and Regazzoni. The race distance was 12 laps, compared to the 14 lap distance for the 1969 race. There was a huge crowd for the race on Sunday- 375,000 and more- and as Graham Hill (Brabham) and Reine Wisell (Lotus) both had problems before the start only 20 cars lined up on the grid. Ickx took the lead from Stewart but the Tyrrell was soon back ahead again and pulling away from the rest with Ickx being chased by Regazzoni, Hulme, Siffert, Peterson and Cevert. Although Ickx was close behind Stewart for about half the first lap, he could not take back the lead- there weren't many places to pass at the Nurburgring. On the second lap Ickx spun off at the Eiskurve corner and Regazzoni went off as he tried to avoid his teammate. This left Stewart with a big lead over Siffert (who had overtaken Hulme). Regazzoni rejoined in third and Peterson (who had also overtaken Hulme) was fourth. The McLaren driver soon fell behind Andretti and Cevert, and the Tyrrell driver soon passed the Ferrari so was up to fifth. In the laps that followed Cevert was the man to watch as he overtook Peterson, Siffert (who soon dropped behind Regazzoni) and then Regazzoni himself after a long battle with the Swiss Ferrari driver- Regazzoni was known to be a hard competitor who was difficult to pass. Thereafter the order remained stable at the front with a Tyrrell 1-2 the result, with Stewart winning his 5th championship Grand Prix of the 1971 season. Regazzoni was third with Andretti catching and passing Peterson for fourth.

For only the third time, the Austrian Grand Prix was a championship round of the Formula One Grand Prix scene. This race, held at the magnificent, very fast and spectacular Österreichring in the rural Styrian mountains 30 minutes from Graz. Jackie Stewart had a mammoth lead in the driver's championship- 51 points over 2nd placed Jacky Ickx's 19 points and Ronnie Peterson's 16 points. If Ickx and Peterson both failed to score here, Stewart would be champion. Jo Siffert took pole in his BRM, followed by Stewart, an ever-improving Cevert, Regazzoni, Fittipaldi and Ickx. Siffert took the lead at the start and successfully held off Stewart's attacks with Regazzoni, Cevert, Ickx and Schenken chasing after them. Both Ferraris were soon in trouble, however, both dropping out of the action with engine trouble. This promoted Cevert to third place and Schenken to fourth. As the race progressed Siffert began to edge away at the front. Cevert was able to close up on Stewart, who was struggling with the handling of his car. On lap 23 Cevert was waved through into second place. On Lap 31, Ickx had retired for good with problems with his Ferrari engine's spark plugs, and so Stewart was now in prime position to become World Champion as Peterson was running around in ninth place and out of the points with serious handling problems- he needed to win the race to stay in the championship hunt. On Lap 36 Stewart's race ended with a broken rear axle. Cevert's charge came to an end on lap 43 when his engine failed and so Fittipaldi moved into second, having overtaken Schenken a few laps earlier. In the final laps Siffert suffered a deflating tire but he was so far ahead that he was able to nurse the car to the line, beating Fittipaldi by just over four seconds for a popular victory. Peterson finished eighth, and the Scottish Stewart was World Champion for the 2nd time in his illustrious career. Niki Lauda, the eventual triple Formula One world champion made his debut in this race in a March; he qualified 21st and retired on lap 20 with handling problems.

The Gold Cup non-championship Grand Prix, again at the challenging English Oulton Park circuit near Manchester was won by veteran John Surtees in his own Surtees car. This race was held 1 week after the Austrian Grand Prix. The Tyrrell team did not enter this event.

The F1 circus came to Italy and the fastest circuit of the year- the Monza Autodrome near Milan. It had been only a year since the death of Jochen Rindt at Monza but the face of Formula 1 had changed. There were still some legal problems between the team and the Italian authorities which resulted from the accident and so Team Lotus did not officially enter the event, although a black and gold Lotus 56 did turn up under the name World Wide Racing. This car was unique in that was powered by an American Pratt & Whitney turbine jet engine. McLaren was also down to just one entry as Denny Hulme was away in the United States for a USAC race in California. Matra was also running only one car as Jean-Pierre Beltoise was still suspended as a result of the sportscar accident in January in Buenos Aires which had cost the life of Ignazio Giunti. The field was bolstered by a third Surtees, entered for Mike Hailwood, a multiple Grand Prix motorcycle champion making the transition to car racing. On the fast sweeps of Monza the V12 cars were very competitive and so Chris Amon was on pole in his Matra with Jacky Ickx alongside in his Ferrari- the Matra V12 had been suffering from an oil churning problem all throughout the season and was way down on power. The Matra engine technicians had solved this problem, and the Matra V12 was now on par with the Ferrari and BRM engines. The second row featured the BRMs of Jo Siffert and Howden Ganley and the first V8 car was the Tyrrell of Francois Cevert, who was fifth on the grid, slightly faster than Ronnie Peterson's March, Jackie Stewart's Tyrrell and Clay Regazzoni's Ferrari. The top 10 was completed by Tim Schenken's Brabham and Henri Pescarolo in Frank Williams's March. At the start of the race Regazzoni made a remarkable start from the fourth row to take the lead and the action behind him was intense as a group of cars slipstreamed around the autodromo, the lead passing backwards and forwards between them. After Regazzoni was toppled, Peterson took the lead and then to Stewart before Regazzoni was back again. Also involved in the fight were Cevert, Siffert, Ickx, Ganley and Gethin. On lap 16 both Stewart and Ickx disappeared with engine failures and two laps later Regazzoni went out as well. While this was happening Hailwood and Amon joined the leading group. Dropping away from the fight were Siffert and Ganley who were both suffering from overheating engines. Siffert did rejoin the leaders a few laps later but then his gearbox began to play up and he dropped back again. For a brief period Amon took the lead and looked like being able to break away but then he lost his visor and dropped back. His engine also began to overheat and so he dropped away from the leading group. The five-car battle for the lead lasted all the way to the finishing line with Gethin getting there by 0.010 secs. The first five cars were all covered by 0.61s. It was the closest finish in the history of the World Championship and the fastest ever race, with an average speed of 150.75 mph. Peterson was second with Cevert third, Hailwood fourth and Ganley fifth. Amon was sixth over half a minute behind in what was certainly one of the most exciting and greatest Grands Prix of all time. Chicanes were then added to Monza's layout for subsequent years; lowering average speeds and effectively eliminating the slipstream battles that highlighted previous Italian Grands Prix at Monza.

Two weeks after the incredible Italian Grand Prix, the F1 circus crossed the Atlantic to eastern Canada. The Canadian round of the championship was held at the fast, flowing and challenging Mosport Park circuit near Canada's largest city, Toronto. Qualifying resulted in World Champion Stewart putting his Tyrrell on pole position ahead of Siffert, Cevert, Fittipaldi, Amon, Peterson, Wisell, and Mark Donohue in a Roger Penske-entered McLaren. The Ferraris were not competitive with Ickx 12th, Andretti 13th and Regazzoni 18th. There was a fatal accident in the Formula Ford race and the Grand Prix was delayed, and by the time the race started it was pouring with rain. Howden Ganley demolished his BRM in the warm-up period before the race and so could not make the start. At the start Stewart went into the lead with Peterson second, chased by Beltoise, Donohue, Fittipaldi, Cevert and the rest. On the third lap Graham Hill crashed his Brabham and five laps later Regazzoni did the same in his Ferrari and lucky to emerge unscathed when the car caught fire. Stewart had a firm grip on the race while Peterson had to fight for second with Beltoise until the Frenchman crashed on lap 16. At the same time Donohue pitted for new goggles but did not lose a place. This left a huge gap between the first two and the rest. Peterson took the lead on lap 18 but on lap 31 Stewart took the lead back while they were going through backmarkers. A few moments later Peterson ran into Eaton's BRM and damaged the front of his car. This upset the balance of the car and Peterson was unable to match Stewart's pace and so the Tyrrell edged away to win by nearly 40 seconds- this was Stewart's sixth championship Grand Prix victory. Donohue finished third on his F1 debut.

Another fortnight later, the F1 circus moved south into the eastern United States to a newly revamped and redesigned Watkins Glen circuit in upstate New York, two and a half hours from Buffalo, four hours from New York City and Philadelphia and five hours from Toronto. The Watkins Glen circuit, originally 2.3 miles long was seeing times get down to the 1 minute 7 second range, and the bottom section of the circuit was almost entirely redesigned, with a whole new pits and paddock complex and an additional mile of new track. The circuit became far more popular than it had been before and was now a spectacular driver's circuit. Jackie Stewart took his sixth pole position of the year for Tyrrell, ahead of Emerson Fittipaldi, Denny Hulme, Clay Regazzoni, Francois Cevert, Jo Siffert, Jacky Ickx and Chris Amon. 29 drivers entered and started the race; Stewart took the lead from Hulme at the start with Cevert jumping up to third place, followed by Regazzoni and Siffert. Fittipaldi made a poor start and was eighth. On the seventh lap Cevert was able to pass Hulme for second place and on lap 14 he moved ahead of Stewart, who was suffering from bad oversteer. Hulme was also having handling problems and he began to drop back, being overtaken by Ickx (who had passed Siffert). Stewart also fell victim to the Ferrari and then Siffert as well. Ickx stalked Cevert until lap 40 when the Ferrari began to fall back with an alternator problem which led to the Belgian's retirement. This moved Siffert to second place and Peterson (who had passed Stewart) to take third. Howden Ganley was fourth with Stewart fifth.

It was Cevert's first World Championship victory and with the Mexican Grand Prix having been cancelled the United States Grand Prix was the last World Championship race of the 1971 season. The FIA cancelled the race because of the previous year's events at the Magdalena Mixhuca Park circuit in Mexico City, where a gigantic crowd turned up to see local hero Pedro Rodriguez compete in the race, and the crowd of some 200,000 were situated in front of the barriers during the race.

There was one more non-championship race to contend, the World Championship Victory Race at Brands Hatch, England 3 weeks after the American round. This race, however, was marred by tragedy. It only lasted for less than half of its intended distance, and there were several incidents. On lap 2, Henri Pescarolo and Reine Wisell collided at the Druids hairpin, with both cars retiring. Then Mike Hailwood and Ronnie Peterson also collided and had to pit for repairs. Hailwood's car was deemed unfit to continue, but Peterson rejoined the race, albeit nearly a lap down. Siffert had fallen several places at the start, but had made his way back to 4th by lap 14. Approaching the fast Hawthorn Bend at high speed on lap 15, Siffert's BRM suffered a mechanical failure which pitched it across the track into an earth bank. The car rolled over and caught fire, trapping Siffert underneath, and he died in the flames- not due to the flames consuming him, but from asphyxiation via inhaling the toxic smoke from the fuel and bodywork-fueled fire. Known as the "Crazy Swiss" thanks to his flat-out driving style and "Seppi" to his friends, Joseph Siffert was 35. The race was stopped with the track blocked, and all the cars were stranded out on the circuit except for John Surtees, who was able to drive around to the pits, his car damaged by debris.